* relocate all SkSG-related files under modules/sksg/
* fix various tidbits to make non-sksg builds possible
* drop obsolete SampleSGInval.cpp
Change-Id: I54e6c5bb1a09f45030fa8d607b3eb3f7cba78957
Reviewed-on: https://skia-review.googlesource.com/130025
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@google.com>
