[Clang][Sema] Prohibit statement expression in the default argument

As statement expression makes no sense in the default argument,
this patch tries to disable it in the all cases.

Please note that the statement expression is a GNU extension, which
means that Clang should be consistent with GCC. However, there's no
response from GCC devs since we have raised the issue for several weeks.
In this case, I think we can disallow statement expressions as a default
parameter in general for now, and relax the restriction if GCC folks
decide to retain the feature for functions but not lambdas in the
future.

Related discussion: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104765

Fixes https://github.com/llvm/llvm-project/issues/53488

Differential Revision: https://reviews.llvm.org/D119609