Bug 1640496 - Fix incorrect FBO state caching when updating external textures. r=sotaro
Bug 1640496 - Fix incorrect FBO state caching when updating external textures. r=sotaro

The `reset_state` method being called after locking external textures
was resetting the cached state, but not actually forcing the GL
state to match.

This could result in cached state getting out of sync with GL. In
this case, we'd end up trying to composite to the external texture
FBO rather than the main framebuffer.

Differential Revision: https://phabricator.services.mozilla.com/D78851

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/3212a1536cbd813777784de35c60e7731404ccc8

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender