Don't destroy blend or color mask state in PLS The browser caches this state, so conditionally destroying it would invalidate the browser's cache. Instead, cache modifications to overridden PLS blend & color mask state in ContextPrivateState, and restore it upon ending PLS. Also update the spec to specify that FRAMEBUFFER_DEFAULT_WIDTH and FRAMEBUFFER_DEFAULT_HEIGHT may be overridden during PLS in ES 3.1. Bug: angleproject:40096838 Change-Id: Ic2c0aa6dc33ada7350e15e27bef22c79ca5f6c7f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6350727 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Alexey Knyazev <lexa.knyazev@gmail.com> Commit-Queue: Chris Dalton <chris@rive.app>