6e313cd781
The accumulated fixes pulled out of the flag flip PR: https://github.com/flutter/engine/pull/50856 * Also fixes tests to make them resilient to StC being on/off. * Fix blending for the cover draw. * Default to depth=1 which is much more reasonable as depth=0 will never draw anything for cover draws. This allows enclosed subpass rendering cases like `Contents::RenderToSnapshot` for filter inputs to work by default and makes mistakes harder. * Use depth+stencil attachments for `Contents::RenderToSnapshot` subpasses to allow for StC draws.