Add test exercising CheckAccessFullyMapped

[bogner]

We need tests in test/Feature/HLSLLib that exercises the CheckAccessFullyMapped function. This should use a Load, Sample, or Gather overload that returns the status of the operation on a resource, and then call CheckAccessFullyMapped on that.

Some interesting corner cases to consider:

• If the status bit is used by something other than CheckAccessFullyMapped, DXC will implicitly call CheckAccessFullyMapped
• If CheckAccessFullyMapped is called on something other than an operation status, DXC will silently treat it as a cast to a bool

[damyanp]

Before we can refine this we need to plan out the work to add support for reserved resources to the offload tester.