Consider relaxing ur_module_handle_t SPIR-V requirement

[FranklandJack]

There seems to be an implicit requirement that ur_module_handle_t objects are SPIR-V modules. From the urProgramCreate entry point:

Create Program from input SPIR-V modules. 

Do we want to restrict the ur_module_handle_t objects to contain SPIR-V only. Or is it possible that higher level language runtimes sitting on top of Unified Runtime could feed it non SPIR-V based intermediate representations for compilation to target specific executables in the adapter via the urModuleCreate -> urProgramCreate path?

[aarongreig]

all references to SPIR-V are replaced with generic references to "IL" in #250