This is in effect a revert of f139ae3d93797, as we have since gained a
more sophisticated way of doing extra IRGen with the addition of
RawAddress in #86923.

Latest diff:
https://github.com/llvm/llvm-project/pull/89154/files/f1ab4c2677394bbfc985d9680d5eecd7b2e6a882..adf9bc902baddb156c83ce0f8ec03c142e806d45

We address two additional bugs here: 

### Problem 1: Deactivated normal cleanup still runs, leading to
double-free
Consider the following:
```cpp

struct A { };

struct B { B(const A&); };

struct S {
  A a;
  B b;
};

int AcceptS(S s);

void Accept2(int x, int y);

void Test() {
  Accept2(AcceptS({.a = A{}, .b = A{}}), ({ return; 0; }));
}
```
We add cleanups as follows:
1. push dtor for field `S::a`
2. push dtor for temp `A{}` (used by ` B(const A&)` in `.b = A{}`)
3. push dtor for field `S::b`
4. Deactivate 3 `S::b`-> This pops the cleanup.
5. Deactivate 1 `S::a` -> Does not pop the cleanup as *2* is top. Should
create _active flag_!!
6. push dtor for `~S()`.
7. ...

It is important to deactivate **5** using active flags. Without the
active flags, the `return` will fallthrough it and would run both `~S()`
and dtor `S::a` leading to **double free** of `~A()`.
In this patch, we unconditionally emit active flags while deactivating
normal cleanups. These flags are deleted later by the `AllocaTracker` if
the cleanup is not emitted.

### Problem 2: Missing cleanup for conditional lifetime extension
We push 2 cleanups for lifetime-extended cleanup. The first cleanup is
useful if we exit from the middle of the expression (stmt-expr/coro
suspensions). This is deactivated after full-expr, and a new cleanup is
pushed, extending the lifetime of the temporaries (to the scope of the
reference being initialized).
If this lifetime extension happens to be conditional, then we use active
flags to remember whether the branch was taken and if the object was
initialized.
Previously, we used a **single** active flag, which was used by both
cleanups. This is wrong because the first cleanup will be forced to
deactivate after the full-expr and therefore this **active** flag will
always be **inactive**. The dtor for the lifetime extended entity would
not run as it always sees an **inactive** flag.

In this patch, we solve this using two separate active flags for both
cleanups. Both of them are activated if the conditional branch is taken,
but only one of them is deactivated after the full-expr.

---

Fixes https://github.com/llvm/llvm-project/issues/63818
Fixes https://github.com/llvm/llvm-project/issues/88478

---

Previous PR logs:
1. https://github.com/llvm/llvm-project/pull/85398
2. https://github.com/llvm/llvm-project/pull/88670
3. https://github.com/llvm/llvm-project/pull/88751
4. https://github.com/llvm/llvm-project/pull/88884

The original change caused widespread breakages in msan/ubsan tests and
causes `use-after-free`. Most likely we are adding more cleanups than
necessary.

Instead of directly pushing the `Destroy`, we should use
`pushFullExprCleanup` which handles conditional branches.
This fixes a backend crash due to
89ba7e183e6e2c64370ed1b963e54c06352211db.

Added minimized crash reproducer.

The IdentifierInfo isn't typically modified. Use 'const' wherever
possible.

Fixes https://github.com/llvm/llvm-project/issues/63818 for control flow
out of an expressions.

#### Background

A control flow could happen in the middle of an expression due to
stmt-expr and coroutine suspensions.

Due to branch-in-expr, we missed running cleanups for the temporaries
constructed in the expression before the branch.
Previously, these cleanups were only added as `EHCleanup` during the
expression and as normal expression after the full expression.

Examples of such deferred cleanups include:

`ParenList/InitList`: Cleanups for fields are performed by the
destructor of the object being constructed.
`Array init`: Cleanup for elements of an array is included in the array
cleanup.
`Lifetime-extended temporaries`: reference-binding temporaries in
braced-init are lifetime extended to the parent scope.
`Lambda capture init`: init in the lambda capture list is destroyed by
the lambda object.

---

#### In this PR

In this PR, we change some of the `EHCleanups` cleanups to
`NormalAndEHCleanups` to make sure these are emitted when we see a
branch inside an expression (through statement expressions or coroutine
suspensions).

These are supposed to be deactivated after full expression and destroyed
later as part of the destructor of the aggregate or array being
constructed. To simplify deactivating cleanups, we add two utilities as
well:
* `DeferredDeactivationCleanupStack`: A stack to remember cleanups with
deferred deactivation.
* `CleanupDeactivationScope`: RAII for deactivating cleanups added to
the above stack.

---

#### Deactivating normal cleanups
These were previously `EHCleanups` and not `Normal` and **deactivation**
of **required** `Normal` cleanups had some bugs. These specifically
include deactivating `Normal` cleanups which are not the top of
`EHStack`
[source1](https://github.com/llvm/llvm-project/blob/92b56011e6b61e7dc1628c0431ece432f282b3cb/clang/lib/CodeGen/CGCleanup.cpp#L1319),
[2](https://github.com/llvm/llvm-project/blob/92b56011e6b61e7dc1628c0431ece432f282b3cb/clang/lib/CodeGen/CGCleanup.cpp#L722-L746).
This has not been part of our test suite (maybe it was never required
before statement expressions). In this PR, we also fix the emission of
required-deactivated-normal cleanups.

To authenticate pointers, CodeGen needs access to the key and
discriminators that were used to sign the pointer. That information is
sometimes known from the context, but not always, which is why `Address`
needs to hold that information.

This patch adds methods and data members to `Address`, which will be
needed in subsequent patches to authenticate signed pointers, and uses
the newly added methods throughout CodeGen. Although this patch isn't
strictly NFC as it causes CodeGen to use different code paths in some
cases (e.g., `mergeAddressesInConditionalExpr`), it doesn't cause any
changes in functionality as it doesn't add any information needed for
authentication.

In addition to the changes mentioned above, this patch introduces class
`RawAddress`, which contains a pointer that we know is unsigned, and
adds several new functions for creating `Address` and `LValue` objects.

This reapplies d9a685a9dd589486e882b722e513ee7b8c84870c, which was
reverted because it broke ubsan bots. There seems to be a bug in
coroutine code-gen, which is causing EmitTypeCheck to use the wrong
alignment. For now, pass alignment zero to EmitTypeCheck so that it can
compute the correct alignment based on the passed type (see function
EmitCXXMemberOrOperatorMemberCallExpr).

This reverts commit d9a685a9dd589486e882b722e513ee7b8c84870c.

The commit broke ubsan bots.

To authenticate pointers, CodeGen needs access to the key and
discriminators that were used to sign the pointer. That information is
sometimes known from the context, but not always, which is why `Address`
needs to hold that information.

This patch adds methods and data members to `Address`, which will be
needed in subsequent patches to authenticate signed pointers, and uses
the newly added methods throughout CodeGen. Although this patch isn't
strictly NFC as it causes CodeGen to use different code paths in some
cases (e.g., `mergeAddressesInConditionalExpr`), it doesn't cause any
changes in functionality as it doesn't add any information needed for
authentication.

In addition to the changes mentioned above, this patch introduces class
`RawAddress`, which contains a pointer that we know is unsigned, and
adds several new functions for creating `Address` and `LValue` objects.

This reapplies 8bd1f9116aab879183f34707e6d21c7051d083b6. The commit
broke msan bots because LValue::IsKnownNonNull was uninitialized.

This reverts commit 8bd1f9116aab879183f34707e6d21c7051d083b6.

It appears that the commit broke msan bots.