[llvm] [SPIR-V] Emit SPIR-V bitcasts between source/expected pointer type (PR #69621)

[Michal Paszkowski via llvm-commits]

michalpaszkowski wrote:

The patch is WIP, apart from the one TODO in the code (which will eliminate adding unnecessary spv_ptrcast calls), I need to fix/adjust 14 LIT tests, and add a test covering the cases fixed in CTS.

https://github.com/llvm/llvm-project/pull/69621