Image accessor DataT and image_format relationship

[Section 4.7.6.1](https://registry.khronos.org/SYCL/specs/sycl-2020/html/sycl-2020.html#_data_type) in the SYCL 2020 specification (Rev. 7) limits the `DataT` template argument in image accessors to `int4` (`vec`), `uint4` (`vec`), `float4` (`vec`), or `half4` (`vec`). However, there are no stated correlation between the `image_format` on the image the accessors are accessing and `DataT`.

Should the specification restrict which specific `DataT` types are allowed when making an accessor from an image with a given `image_format` or is it intentional that images can be accessed as another type than suggested by the `image_format`?

Start with Section 4.7.6.1 of the linked SYCL 2020 specification and compare its allowed DataT types with the image_format definitions. Determine whether the specification needs an explicit relationship or intends to allow other type and format combinations; done means documenting the resolved rule in the relevant specification text.

Written by the indexing model from the issue text.