[Validation] Add an assert to make sure no dxil opcodes are left unvalidated.

Is your feature request related to a problem? Please describe.
ValidateDxilOperationCallInProfile and ValidateHandleArgsForInstruction inside of DxilValidation.cpp only list a subset of opcodes in the switch statement that determines how to validate a specific opcode. The default case (if no opcodes are matched) is empty, and there's no indication that an opcode isn't being validated by the function.

Describe the solution you'd like
Both of these functions should have a DXAssert in the default case of these switch statements to alert the user when an opcode that should be validated isn't being validated.

Describe alternatives you've considered
It may not be necessary to implement a statement for the default case if we can logically prove that these functions will never be called for certain intrinsics (e.g., ValidateHandleArgsForInstruction shouldn't be called on an intrinsic that doesn't have some *Handle argument). In this case, a comment should be left that explains why there is nothing in the default case.

Start in DxilValidation.cpp by reading ValidateDxilOperationCallInProfile and ValidateHandleArgsForInstruction, especially their opcode switch statements and default cases. Determine whether each default can be reached for an opcode requiring validation. Done means both cases either assert on an unvalidated opcode or contain a comment explaining why no validation is needed.