[llvm] [RFC][SPIR-V] Add intrinsics to convert to/from ap.float (PR #164252)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

The IRTranslator change is incomplete, this is missing the new G_* opcodes. Also would require a mirrored SelectionDAGBuilder patch. The amount of codegen support here should either be complete, or moved to a later patch 

https://github.com/llvm/llvm-project/pull/164252