Make AutoBackendTexture remember which context it was created with

... and use that stored context when creating an SkImage or SkSurface.

As per I52e1d831f2d195cddb21c2e7a1e820059fe2a137 we no longer share
buffers between contexts, and this aligns with Graphite's need to know
the context that a backend texture was created with to clean it up in
ABT's destructor.

Test: manually validated core CUJs + existing tests (refactor)
Bug: b/293371537
Bug: others listed in I52e1d831f2d195cddb21c2e7a1e820059fe2a137
Change-Id: I7d4b0b95216b0529be72cfb7c2788c592a77ed0e