Clip text geometrically when possible.

Currently when we clip text we can't batch the clipped text with non-clipped text.
By modifying the quads and texCoords we can produce the same effect, and allow batching.
Includes some minor text code cleanup.

Bug: skia:6990
Change-Id: Ibfd4bc2fdc2d7680071e2abddd4d77fc3017e3d3
Reviewed-on: https://skia-review.googlesource.com/60780
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
7 files changed