split working-format filter into two parts
split working-format filter into two parts

The old filter represented the whole (xform -> child -> xform) sandwich,
where this new one represents just one xform, with the factory now using
Compose() to piece the sandwich together.

This is conceptually simpler, which is nice, and we should also be able
to use this to replace SkSRGBGammaColorFilter (next CL).

Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Change-Id: I6dee3c968329ab74f24e01fcdb82872141cdd496
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/371456
Reviewed-by: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>
Commit-Queue: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>

google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia