[SYCL] Add basic verification for accessor type

When processing accessors, we use the template parameters to make various assumptions. It is important to ensure these parameters are defined as expected, to prevent the compiler from crashing due to a rogue library implementation.

An attempt was made to fix this here - https://github.com/intel/llvm/pull/4099

But it has been decided to wait for https://github.com/intel/llvm/pull/3892 to be implemented instead, since the checks can be done as part of attribute handling instead of the device compiler.

See - https://github.com/intel/llvm/pull/4099#issuecomment-879988921