[clang] Fix crash when passing a braced-init list to a parentehsized aggregate init expression

The previous code incorrectly assumed that we would never call
warnBracedScalarInit(...) with a EK_ParenAggInitMember. This patch fixes
the bug by warning when a scalar member is initialized via a braced-init
list when performing a parentehsized aggregate initialization. This
behavior is consistent with parentehsized list aggregate initialization.

Fixes #63008

Reviewed By: shafik

Differential Revision: https://reviews.llvm.org/D151763