Adds test that checks whether LLDB correctly infers the
alignment of packed structures. Specifically, the
`InferAlignment` code-path of the `ItaniumRecordLayoutBuilder`
where it assumes that overlapping field offsets imply a
packed structure and thus sets alignment to `1`. See discussion
in https://github.com/llvm/llvm-project/pull/93809.

While here, also added a test-case where we check alignment of
a class whose base has an explicit `DW_AT_alignment
(those don't get transitively propagated in DWARF, but don't seem
like a problem for LLDB).

Lastly, also added an XFAIL-ed tests where the aforementioned
`InferAlignment` kicks in for overlapping fields (but in this
case incorrectly since the structure isn't actually packed).

Part of fixes for #72913.

clang emits `DW_AT_alignment` attribute, however LLDB didn't respect it,
resulting in incorrect RecordDecls built by lldb.

This only fixes non-inheritance cases. The inheritance case will be
handled in a follow-up patch.

Currently the ItaniumRecordLayoutBuilder when laying out base classes has the virtual
and non-virtual bases mixed up when pulling the base class layouts from the external source.

This came up in an LLDB bug where on arm64 because of differences in how it deals with
tail padding would layout the bases differently without the correct layout from the
external source (LLDB). This would result in some fields being off by 4 bytes.

Differential Revision: https://reviews.llvm.org/D83008