[HLSL] Implement availability diagnostic - Strict mode

[hekota]

Implement strict mode of the availability diagnostic.

In addition to the default mode diagnostics, the strict mode will also emit an error during parsing of any callee of a CallExpr that has availability annotation that marks it as unavailable for the target shader model and stage (for non-library shaders) or the target shader model (for library shaders) - regardless of reachability.

A user enables strict mode by passing -fhlsl-strict-diagnostics.

See HLSL Availability Diagnostic spec for more details.