Define MediaFormat crop-related constants

MediaFormat used literals "crop-left", "crop-right", crop-bottom
and crop-top. Define appropriate MediaFormat.KEY_XXX for these.

Bug: 178687730
Test: build, boot
Test: atest android.media.codec.cts.EncodeDecodeTest
Change-Id: I1782caa5ff320d3dca19272c5532466199ef72f0