Add Raster Pipeline op for swizzled copies.

This will let us perform masked, swizzled writes into value slots
via a single lvalue-store operation.

Change-Id: If3417fa104d13b2669d6dec83ff3bbc19bc95d20
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/646738
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
4 files changed