Adding aliases for sycl::vec and sycl::marray of size 1

Since in OpenCL there are types of size 1 https://registry.khronos.org/OpenCL/sdk/1.0/docs/man/xhtml/vectorDataTypes.html which are represented as for example `cl_float`, along `cl_float2`, `cl_float4`, etc.

We could do the same for `sycl::mfloat`, along `sycl::mfloat2`, etc. https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#_aliases_2

For `sycl::vec` https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#_aliases we would have a keyword conflict on `sycl::float` so we could use `sycl::float1` instead.

Perhaps we could use `sycl::mfloat1` instead of `sycl::mfloat` by symmetry and have the `1` everywhere in `marray` alias of size 1 too, to be very explicit.

Start with the OpenCL vector data type link and the SYCL specification sections for aliases cited in the issue. Resolve whether size-one aliases should use mfloat, mfloat1, and float1, and whether marray aliases also include 1; done means the specification records one consistent naming scheme.

Written by the indexing model from the issue text.