[clang] Replace uses of CGBuilderTy::CreateElementBitCast (NFC)

Partial progress towards replacing `CreateElementBitCast`, as it no
longer does what its name suggests. Either replace its uses with
`Address::withElementType()`, or remove them if no longer needed.

Reviewed By: barannikov88, nikic

Differential Revision: https://reviews.llvm.org/D153314