* [android] External textures must be rescaled to fill the canvas
- After composition, we have a tight box that we need to fill.
- Video decoders typically operate using output buffers that are a whole
number of blocks (vertically and horizontally). This fixes
https://github.com/flutter/flutter/issues/34641 where the decoded
dimensions are rounded up.
- The cropping information for the current frame arrives in the form of
`SurfaceTexture.getTransformMatrix`. When we apply this transform we
need to account for the fact that we have already composited. This
means that in cases where the scaleX, scaleY are less than 1, we need
to rescale the image. We do this while preserving the aspect ratio.
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