This reverts commit f456423cfb820d07bb36e9a8979e3d75cc9d8d76.
This is being reverted because it caused flutter/flutter#45098
(images don't load on iOS).
When gr context is changed (this happens when sending the app to the background and then to the foreground) we need to update it for all the platform view overlay surfaces.
The update logic was caching the previous gr context to figure if it had to be updated, but after updating it for a given overlay we were updating the cached context. In apps with multiple platform views this will result in overlays with a stale gr context.
This fixesflutter/flutter#36437
And I believe it should fixflutter/flutter#36999 as well (though I don't have repro code to verify).
Having 2 or more platform views simultaneously in the layer tree was crashing immediately on iOS with GL backend.
This regressed in #11070 which passed gl_context to a function in a loop using std::move (which meant on the second iteration the caller is no longer the owner of the field).
I added a scenarios_app test, though this test doesn't run on a physical device on CI so it would have only caught the problem when running locally (flutter/flutter#43852).
