[clang] fix transformation of template arguments of 'auto' type constraints

See PR48617.

When assigning the new template arguments to the new TypeLoc, we were looping
on the argument count of the original TypeLoc instead of the new one,
which can be different when packs are present.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D109406