[analyzer] StackAddrEscapeChecker: strip qualifiers from temporary types.

With the new support for trivial copy constructors, we are not always
consistent about whether a CXXTempObjectRegion gets reused or created
from scratch, which affects whether qualifiers are preserved. However,
we probably don't care anyway.

This also switches to using the current PrintingPolicy for the type,
which means C++ types don't get a spurious 'struct' prefix anymore.

llvm-svn: 176068