Provides a number of template trait types for Reactor primitive types:

CToReactorT<T> transforms the C-type (T) into a suitable Reactor equivalent. Pointer types are now generalized, allowing for translations of T** types.

IsRValue<T>::value and IsLValue<T>::value are true iff T is of the respective Reactor type.

ReactorType<T> resolves to the corresponding LValue Reactor type for T, where T can be a C-type, RValue or LValue.

ValueOf<T> returns a rr::Value* for a C-value, RValue or LValue. This is now used by a single definition of Return(), fixing bad type coercion which in turn produced illegal LLVM IR.

CanBeUsedAsReturn<T>::value is true iff T can be used as a function return type.
CanBeUsedAsParameter<T>::value is true iff T can be used as a function parameter type.
Function signatures are now statically checked that all parameter types and the return type are valid, providing a human readable error message if an invalid type is used (verified on gcc, clang and msvc).

Added a whole bunch of static asserts in ReactorUnitTests.cpp to sanity check the templates.

Bug: b/131914569
Change-Id: I3267354d6a3f68545079365a657757969ec0047d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/30455
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>