"Reapply "[Sema] Fix crash on invalid code with parenthesized aggrega… (#76833)

…te initialization" (#76272)""

With updates the libc++ tests.

This reverts commit 2205d233 and relands
86dc6e15 and
7ab16fb5.

Original commit was reverted because of failing libc++ tests, see #76232
for the discussion.

The errors in the tests are spurious in the first place (coming from
initialization of invalid classes), so update the tests to match new
behavior that does not show those errors.

The original patch was written by @ilya-biryukov 

To fix the CI two libc++ tests are temporary disabled for clang-18.