Fix subpixel image filtering in CPU backend

Long ago, the CPU backend decided that all subpixel translation could be
ignored (for performance). Many years ago, we corrected that behavior
for SkImageShader, so that filtering a subpixel-translated image would
no longer snap to pixels.

Surprisingly, drawImage (and friends) still has the same behavior. The
new GM drew a crisp checkerboard for the first two boxes prior to the
fix.

Bug: b/41322892
Change-Id: Iff9071dae1f79d9bcef09f7ecb282e997720069e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/820178
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
2 files changed