[SPIR-V] Add support for SPV_INTEL_masked_gather_scatter extension (#185418)
Fixes the first bullet in #184638
Corresponding patch to add support for vector operands in
OpConvertPtrToU/OpConvertUToPtr operations in spirv-val:
https://github.com/KhronosGroup/SPIRV-Tools/pull/6575
SPIR-V extension reference used:
https://github.com/KhronosGroup/SPIRV-Registry/blob/278044a51fee280bfc91322cdb55b51357db5cb8/extensions/INTEL/SPV_INTEL_masked_gather_scatter.asciidoc