Support converting pointers from opaque to typed

Support converting pointers from opaque to typed

Using the pointer type analysis we can re-constitute typed pointers and
populate the correct types in the bitcasts throughout the IR.

This doesn't yet handle all cases, but this should be illustrative as
to the dirction and feasability of
the solution.

Reviewed By: pete

Differential Revision: https://reviews.llvm.org/D122270