Rename outputSwizzle->writeSwizzle.

It is also used for writes to surfaces other than fragment shader
output. e.g. clears.

Change-Id: Id1eb79be6d1a8aed936456bffa59dee32661cec8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/280344
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
43 files changed