Enhance mobile suspend MainLoop notifications

[ztc0611]

Implements godotengine/godot-proposals#8453

iOS:

Adds NOTIFICATION_APPLICATION_RESUMED and NOTIFICATION_APPLICATION_PAUSED on iOS, as well as making the application being switched from also fire NOTIFICATION_APPLICATION_FOCUS_OUT and NOTIFICATION_APPLICATION_FOCUS_IN upon returning.

Android:

Makes the application being switched from fire NOTIFICATION_APPLICATION_FOCUS_OUT and NOTIFICATION_APPLICATION_FOCUS_IN upon returning.

Be mindful of godotengine/godot-proposals#8453 (comment), there may be complications with DeX mode that need to be ironed out.

[akien-mga]

It would be better to have the Android and iOS implementations in the same PR/commit, so that we don't risk introducing significant platform support differences. If you could only implement one, it's fine to have a PR for it, but since you did both it makes sense to land that change all at once.

[ztc0611]

@Calinou thoughts?

I don't feel strongly one way or the other here, I just want to make sure everyone is on the same page to avoid future confusion.

[Calinou]

I'd follow Akien's judgement here, so that it's easier to compare the Android and iOS code added in the same PR.

[ztc0611]

Merged

[m4gr3d]

The Android section looks good.

[AThousandShips]

Please squash your commits into one, see here

[ztc0611]

Done 🙂

[AlexBowring]

Any update on this? I believe this feature is exactly what i'm looking for in my own game, so would be great to see this merged

[YuriSizov]

Any update on this?

The iOS part still needs to be reviewed and we don't have a dedicated iOS maintainer, so it takes some time.

[ztc0611]

Came back from that notification and forgot I should have included the rationale for this.

[b]Note:[/b] On iOS, you only have approximately 5 seconds to finish a task started by this signal. If you go over this allotment, iOS will kill the app instead of pausing it.

The source for that claim added to the docs is this, there might be a better way to word it but that might make review a bit easier. I think this is relevant information because it would probably be hard for someone deep into a Godot project to think to check Apple's docs for applicationDidEnterBackground().

[akien-mga]

Thanks!