Let LayerDrawable choose the best scaling filter for readback.

The check used in Readback.cpp did not take the transformation
matrix into account for judging whether the copy was scaling.

libs/hwui/pipeline/skia/LayerDrawable.cpp already incorporates
the logic to detect non-scaling copy, so we can just let it
check the condition. This version regards 90-degree rotation
without size change as non-scaling and disables filters.

Bug: 151126720
Bug: 150839078
Test: atest android.view.cts.PixelCopyTest
Change-Id: I69e987e6a2e48299c5e579f8c218c42a724dc606