[Clang] Fix dependency of SourceLocExpr. (#78436)

SourceLocExpr that may produce a function name are marked dependent so that the non-instantiated
name of a function does not get evaluated.

In GH78128, the name('s size) is used as
template argument to a `DeclRef` that is not otherwise dependent, and therefore cached and not transformed when the function is
instantiated, leading to 2 different values existing at the same time for the same function.

Fixes #78128