Remove extra spaces and comments from sksl fragments

This also adds a presubmit to avoid this creeping into src/

Prior art: http://review.skia.org/578578 which removed ~35kb
of whitespace and comments - it all adds up!

Bug: b/40041065
Change-Id: I9844dbfdeeb8ba13ae44121f7ac743ce3aaf4708
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/961316
Commit-Queue: Nicolette Prevost <nicolettep@google.com>
Auto-Submit: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Nicolette Prevost <nicolettep@google.com>
75 files changed