In order to have common code to create a image from a buffer, that we
plan to use later on a new codepath.
This refactor adds three new methods:
* One that gathers all the info required to create the structures and
implement the operation
* One that creates the image from the buffer, based on that info
* One that creates a BlitRegion from that info
This seems like too much splitting, but we needed to do it in this
way, because we can't ensure that future uses of this common code
would use a BlitRegion.
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23864>
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