[lldb] Rename RecursiveDecentFormatter to RecursiveDescentFormatter (NFC)

The problem was in calling GetLoadAddress on a value in the error state,
where `ValueObject::GetLoadAddress` could end up accessing the
uninitialized "address type" by-ref return value from `GetAddressOf`.
This probably happened because each function expected the other to
initialize it.

We can guarantee initialization by turning this into a proper return
value.

I've added a test, but it only (reliably) crashes if lldb is built with
ubsan.

Introduces a `member` property to `SBValue`. This property provides pythonic access to a
value's members, by name. The expression `value.member["name"]` will be an alternate
form form of writing `value.GetChildMemberWithName("name")`.

The ValueObjectConstResult classes that back expression result variables
play a complicated game with where the data for their values is stored.
They try to make it appear as though they are still tied to the memory
in the target into which their value was written when the expression is
run, but they also keep a copy in the Host which they use after the
value is made (expression results are "history values" so that's how we
make sure they have "the value at the time of the expression".)

However, that means that if you ask them to cast themselves to a value
bigger than their original size, they don't have a way to get more
memory for that purpose. The same thing is true of ValueObjects backed
by DataExtractors, the data extractors don't know how to get more data
than they were made with in general.

The only place where we actually ask ValueObjects to sample outside
their captured bounds is when you do ValueObject::Cast from one
structure type to a bigger structure type. In
https://reviews.llvm.org/D153657 I handled this by just disallowing
casts from one structure value to a larger one. My reasoning at the time
was that the use case for this was to support discriminator based C
inheritance schemes, and you can't directly cast values in C, only
pointers, so this was not a natural way to handle those types. It seemed
logical that since you would have had to start with pointers in the
implementation, that's how you would write your lldb introspection code
as well.

Famous last words...

Turns out there are some heavy users of the SB API's who were relying on
this working, and this is a behavior change, so this patch makes this
work in the cases where it used to work before, while still disallowing
the cases we don't know how to support.

Note that if you had done this Cast operation before with either
expression results or value objects from data extractors, lldb would not
have returned the correct results, so the cases this patch outlaws are
ones that actually produce invalid results. So nobody should be using
Cast in these cases, or if they were, this patch will point out the bug
they hadn't yet noticed.

710276a2505514634a7cc805461b1219dcef9337 added settings to control
leading zeros but the initial test case assumed a 64 bit target.

This test was reported as failing by https://lab.llvm.org/buildbot/#/builders/68/builds/60172. The fix is very simple. We need to invoke the correct setting.

As suggested by Greg in https://github.com/llvm/llvm-project/pull/66534,
I'm adding a setting at the Target level that controls whether to show
leading zeroes in hex ValueObject values.

This has the benefit of reducing the amount of characters displayed in
certain interfaces, like VSCode.

All Python files in the LLVM repository were reformatted with Black [1].
Files inside the LLDB subproject were reformatted in 2238dcc39358. This
patch updates a handful of tests that were added or modified since then
and weren't formatted with Black.

[1] https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style/68257

as we don't in general know where the extra data should come from.

Differential Revision: https://reviews.llvm.org/D153657