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Replace "concept based polymorphism" with simpler PImpl idiom.

This pursues two goals:
* Enforce static type checking. Previously, target implementations hid
base class methods and type checking was impossible. Now that they
override the methods, the compiler will complain on mismatched
signatures.
* Make the code easier to navigate. Previously, if you asked your
favorite LSP server to show a method (e.g. `getInstructionCost()`), it
would show you methods from `TTI`, `TTI::Concept`, `TTI::Model`,
`TTIImplBase`, and target overrides. Now it is two less :)

There are three commits to hopefully simplify the review.

The first commit removes `TTI::Model`. This is done by deriving
`TargetTransformInfoImplBase` from `TTI::Concept`. This is possible
because they implement the same set of interfaces with identical
signatures.

The first commit makes `TargetTransformImplBase` polymorphic, which
means all derived classes should `override` its methods. This is done in
second commit to make the first one smaller. It appeared infeasible to
extract this into a separate PR because the first commit landed
separately would result in tons of `-Woverloaded-virtual` warnings (and
break `-Werror` builds).

The third commit eliminates `TTI::Concept` by merging it with the only
derived class `TargetTransformImplBase`. This commit could be extracted
into a separate PR, but it touches the same lines in
`TargetTransformInfoImpl.h` (removes `override` added by the second
commit and adds `virtual`), so I thought it may make sense to land these
two commits together.

Pull Request: https://github.com/llvm/llvm-project/pull/136674

... to clarify ownership, aligning with other parameters. Using
`std::unique_ptr` encourages users to manage `createMCInstPrinter` with
a unique_ptr instead of a raw pointer, reducing the risk of memory
leaks.

* llvm-mc: fix a leak and update llvm/test/tools/llvm-mc/disassembler-options.test
* #121078 copied the llvm-mc code to CodeGenTargetMachineImpl and made
  the same mistake. Fixed by 2b8cc651dca0c000ee18ec79bd5de4826156c9d6

Using unique_ptr requires #include MCInstPrinter.h in a few translation
units.

* Delete a createAsmStreamer overload I deprecated in 2024
* SystemZMCTargetDesc.cpp: rename to `createSystemZAsmStreamer` to fix
  an overload conflict.

Pull Request: https://github.com/llvm/llvm-project/pull/135128

For many targets, llvm-objdump and llvm-mc
(https://reviews.llvm.org/D103004) support -M no-aliases (e.g.
`RISCVInstPrinter::applyTargetSpecificCLOption`).

This patch implements -M for llc.

While here, rename "DisassemblerOptions" in llvm-mc to the more
appropriate "InstPrinterOptions". For llvm-mc --assemble, there is no
disassembler involved.

Pull Request: https://github.com/llvm/llvm-project/pull/121078

Following discussions in #110443, and the following earlier discussions
in https://lists.llvm.org/pipermail/llvm-dev/2017-October/117907.html,
https://reviews.llvm.org/D38482, https://reviews.llvm.org/D38489, this
PR attempts to overhaul the `TargetMachine` and `LLVMTargetMachine`
interface classes. More specifically:
1. Makes `TargetMachine` the only class implemented under
`TargetMachine.h` in the `Target` library.
2. `TargetMachine` contains target-specific interface functions that
relate to IR/CodeGen/MC constructs, whereas before (at least on paper)
it was supposed to have only IR/MC constructs. Any Target that doesn't
want to use the independent code generator simply does not implement
them, and returns either `false` or `nullptr`.
3. Renames `LLVMTargetMachine` to `CodeGenCommonTMImpl`. This renaming
aims to make the purpose of `LLVMTargetMachine` clearer. Its interface
was moved under the CodeGen library, to further emphasis its usage in
Targets that use CodeGen directly.
4. Makes `TargetMachine` the only interface used across LLVM and its
projects. With these changes, `CodeGenCommonTMImpl` is simply a set of
shared function implementations of `TargetMachine`, and CodeGen users
don't need to static cast to `LLVMTargetMachine` every time they need a
CodeGen-specific feature of the `TargetMachine`.
5. More importantly, does not change any requirements regarding library
linking.

cc @arsenm @aeubanks