Draft: egl/wayland: Try to avoid buffer reallocations on surface feedback

This is related to a discussion regarding the optimal implementation of the protocol at wayland/wayland-protocols#90

If the currently used modifier is considered optimal by the compositor, don't force a buffer reallocation. This allows compositors to implement their feedback behaviour in a more transparent way without triggering frequent reallocations in clients. Reallocations will still happen if the compositor signals that the current one is not optimal by resending the feedback with the current modifier move to a later tranche.

This notably benefits the current implementations in Mutter and Sway.