[Feature Request] Add flag to disable all HLSL intrinsics when using `-spirv`

[Przemog1]

Is your feature request related to a problem? Please describe
When using -spirv to generate SPIR-V from HLSL, we sometimes want to write everything in Inline-SPIR-V and avoid relying on HLSL intrinsics. Currently, there is no way to disable all HLSL intrinsics, which forces us to work around their limitations. HLSL intrinsics often fall short, for example:

• Cannot perform atomics on 64-bit values.
• Missing double overloads for sqrt.
• (HLSL intrinsic will match everything and anything even forward declared template functions #7971)
  etc

Describe the solution you'd like
A compiler flag (to be used together with -spirv) that completely disables HLSL intrinsics. This would allow developers to rely fully on Inline-SPIR-V without waiting for HLSL/Clang coverage to improve.