[svg] Fix mask edge artifacts
[svg] Fix mask edge artifacts

Per spec, the explicit <mask> bounds [x,y,w,h] are used to also clip
the content (the actual mask geometry may extend beyond these bounds).

This clip is currently scoped such that it applies both to the mask
layer and the content layer.  When the clip is not pixel-aligned,
we're anti-aliasing both layers' edges -- which darkens the composition
result (producing dark hairlines around the mask).

Push the clip down such that it applies to content only.

Change-Id: I32169e2b6dc9685e50a51c6b22cfaaac1a897239
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/354217
Commit-Queue: Florin Malita <a8262bf13ea8c26821e91ea9bca6740a77c96dcd@google.com>
Reviewed-by: Tyler Denniston <293ae2d31b7e9da32c4fb58bdaaed1f4bef4c6e7@google.com>

aosp-mirror/platform_external_skia,google/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,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