Merge 4 release notes into RELEASE_NOTES.md

Change-Id: I3286524de9349c984a2da1ed8df94d39a2c8a0b1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1140377
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Heather Miller <hcm@google.com>
5 files changed