Use analytic coverage FPs with MSAA
Use analytic coverage FPs with MSAA

This addresses the performance regressions on vkmsaa8 and other msaa
locked devices from the new GrClipStack. Now that elements are forced
to upgrade to AA, this allows axis-aligned anti-aliased rects to be
implemented as an FP instead of generating a stencil mask.

This is an alternative to https://skia-review.googlesource.com/c/skia/+/317772
and does not appear to regress visual quality.

Bug: skia:10370
Change-Id: If89b4368fb0c684851e6648bf70e1b608e19852c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317836
Reviewed-by: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>
Reviewed-by: Chris Dalton <ef7fc3a08ada7d31f16e9a18b5f3c728256e041e@google.com>
Commit-Queue: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>

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