[analyzer] Fix static_cast on pointer-to-member handling

This commit fixes bug #48739. The bug was caused by the way static_casts
on pointer-to-member caused the CXXBaseSpecifier list of a
MemberToPointer to grow instead of shrink.
The list is now grown by implicit casts and corresponding entries are
removed by static_casts. No-op static_casts cause no effect.

Reviewed By: vsavchenko

Differential Revision: https://reviews.llvm.org/D95877