Rename our SYCL aliases floatN to FloatN

Rename our SYCL aliases floatN to FloatN

Main reasons:

- Clearly separate our types (or aliases) from native types. This will
  likely make later changes (e.g., in scope of #3312) easier.
- Enable hipSYCL build by avoiding clashes of multiple floatN in the
  global namespace.

Refs #3312, #3923