[C++][Sema] Ignore top-level qualifiers in casts

Ignore top-level qualifiers in casts, which fixes issues in reinterpret_cast.

This rule comes from [expr.type]/8.2.2 which explains that casting to a
pr-qualified type should actually cast to the unqualified type. In C++
this is only done for types that aren't classes or arrays.

Fixes: PR49221

Reviewed By: Anastasia

Differential Revision: https://reviews.llvm.org/D102689