[InferAddressSpaces] Fix assert on invalid bitcast placement

Similar to the problem in 0bb25b46, bitcasts that are inserted must
dominate all uses. When rewriting "values" with "new values" that have
the updated address space, we may replace the "new value" with a bitcast
if one of the original users is an addresspace cast. This bitcast must
be inserted before ALL users, not only before the addresspace cast.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D122964