Moved _Tile from Image to ImageFile

[radarhere]

Suggestions for python-pillow#6486. I'm optimistic that this will be my last PR for this.

• Renamed data_offs to offset, to match the name of the variable in _Tile
• In _Tile, args is not always a tuple. It might also be a string or None
• While I previously added support for 8 bit RGB images, I forgot about the masks, and presumed that it would grayscale. Since that was flawed, I'm removing it here. Instead, Support arbitrary masks for uncompressed RGB DDS images python-pillow/Pillow#7589 will provide support for general masks and RGB bitcounts.
• Moved _Tile from Image to ImageFile and . In the main branch, there is no use of tiles in Image, only in ImageFile. I've also removed the change to __setstate__() in Image, because this is covered in ImageFile's __setstate__().
• I've updated some constants after looking at https://microsoft.github.io/DirectX-Specs/d3d/SamplerFeedback.html

DXGI_FORMAT_SAMPLER_FEEDBACK_MIN_MIP_OPAQUE = 189,
DXGI_FORMAT_SAMPLER_FEEDBACK_MIP_REGION_USED_OPAQUE = 190,