Store original task width and height instead of scale

Store the original task snapshot size instead of the scale from which
the bitmap was saved. This simplifies the logic around restoring and
saving from the proto, as both the reduced scale and full scale
snapshots make use and share the same state.

Also remove scale from TaskSnapshot, and remove and reducedScale from
TaskSnapshot.Builder.

Test: TaskSnapshotCacheTest
Test: TaskSnapshotControllerTest
Test: TaskSnapshotPersisterLoaderTest
Test: TaskSnapshotSurfaceTest
Bug: 148491788
Bug: 148617404
Bug: 142063079
Change-Id: I1dccaba87c3d8b95bf4156f41f9fd5d40019f675