[AArch64][SVE] Fix handling of stack protection with SVE

Fix a couple of things that were causing stack protection to not work
correctly in functions that have scalable vectors on the stack:
 * Use TypeSize when determining if accesses to a variable are
   considered out-of-bounds so that the behaviour is correct for
   scalable vectors.
 * When stack protection is enabled move the stack protector location
   to the top of the SVE locals, so that any overflow in them (or the
   other locals which are below that) will be detected.

Fixes: https://github.com/llvm/llvm-project/issues/51137

Differential Revision: https://reviews.llvm.org/D111631