[llvm] [SPIRV] Add support for `bfloat16` atomics via the `SPV_INTEL_16bit_atomics` extension (PR #166257)

[Alex Voicu via llvm-commits]

https://github.com/AlexVlx commented:

> IIRC there is a later mechanism which checks which extension is allowed for the current target and raises an "SPIR-V module cannot be satisfied" error if an extension/capability is showing but is not allowed. 

Right, but that is somewhat opaque i.e. the error message at the moment is an approximation of "something happened". We should look at refactoring the pass itself at some point to rather go through the Diag infra, but that feels like a separate PR / piece of work, as currently all of the extension related stuff is done via `report_fatal_error`.

https://github.com/llvm/llvm-project/pull/166257