Batch 9-patches in a single mesh whenever possible

This change also fixes the way batched bitmaps were handled
inside a layer. The layer is now correctly dirtied to minimize
the amount of pixels to blend.

Fix alpha, mode and opaque computations for DrawPatchOp.

Change-Id: I1b6cd581c0f0db66c1002bb4fb1a9811e55bfa78
8 files changed