Add a kWireframe flag to GrPipeline

Adds the flag to GrPipeline, as well as a 'w' keystroke in viewer for
toggling the alternate global wireframe mode.

Change-Id: I385c31320a5fa2cec79b527a91fa876b19cdff89
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/260747
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
10 files changed