[clang][AST] Propagate the value-dependent bit for VAArgExpr.

Fixes https://github.com/llvm/llvm-project/issues/62711

We never set the value-dependent bit for the VAArgExpr before this
patch, this was fine becase the dependent-type TypoExpr was always
resolved before checking the operands (see https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaExpr.cpp#L21173-L21180)

Now we have enabled the dependence by default for C, the typo expr is
not early resolved before checking rather than delayed (share the same
codepath with C++).

The fix is to propagate the value-dependent bit for VAArgExpr where it contains
a TypoExpr, so that the AST node can be handled properly.

Differential Revision: https://reviews.llvm.org/D150955