Bug
1706561 Part 5: Intern polygon data for image masks, and retrieve for hit tests. r=gw
This moves the polygon data out of the ClipItemKind and ClipItemKeyKind enums,
which reduces bloat, which improves access times for scenes with lots of
clips -- even if they don't use image mask clips. The SceneBuilder interns
polygons when they arrive alongside image mask clips, and the HitTestingScene
retrieves them when it's time to build the hit test nodes.
Differential Revision: https://phabricator.services.mozilla.com/
D114558