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

[Dmitry Sidorov via llvm-commits]

MrSidims wrote:

@arsenm @nikic @efriedma-quic @maarquitos14 thanks for the feedback! I've changed description of the intrinsics, clarifying semantics, hope I haven't missed anything. 

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