Define SK_SUPPORT_LEGACY_ALPHA_BITMAP_AS_COVERAGE am: 66e866e7f6

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/skia/+/19291567

Change-Id: I9cf7af8305cc6416aa9338e7ee85c5a51584d152
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>