[3.0.x back port] VideoToolbox module and iOS display : Fix to prevent a fallback to avcodec

It appears that the vout display fails to initialize while app is entering foreground, returning an error to videotoolbox module and leading to a fallback to software decoding with avcodec.

Allowing vout creation while app is either in inactive or active state seems to fix the issue encountered in vlc-ios#1240 (closed).

The display can be created when the application state is active or inactive. Inactive state actually happens when the application comes back from background and becomes active just after a very short amount of time. Hence we should allow vout initialization only when application state is not background.

It appears the additional changes in !1175 (b0228902) might not be necessary to fix the issue, but I find those changes quite interesting because display failure might not trigger a fallback to another decoder.

This is a 3.0.x back port for !1174 (merged)