Multiple improvements to converter 3 to 4.

[FeralBytes]

Catch:
Thread.is_active() to is_alive().
Signal "idle_frame" to "process_frame"
Settings for Window size width/height to viewport_width/height. OS.real_window_size(), get_screen_size(), get_window_size() to DisplayServer equivalents.
OS.get_system_time_secs() to Time.get_time_dict_from_system()['seconds'].

I currently removed the fix for: String.plus_file() to path_join() because the Linux mono build says the function does not exist.
I removed get_network peer fix because it too does not match a direct function call since it is actually a method call which returns an object to call a second method in order to fix the Godot 3 sequence. get_network_peer() -> get_multiplayer().get_multiplayer_peer()

I also think it would be easy to fix:

• Engine.editor_hint to Engine.is_editor_hint()
• MainLoop.NOTIFICATION_WM_QUIT_REQUEST to NOTIFICATION_WM_CLOSE_REQUEST
• MainLoop.NOTIFICATION_ to NOTIFICATION_

Although I think it would be easy to implement the above I also think I would break your code trying to do so.
Everything else that I mentioned here will be much more difficult.

[FeralBytes]

Missing GDScript function in pair (get_network_peer - ===> get_multiplayer().get_multiplayer_peer <===)
This failure is valid, but not sure how to handle that change, any suggestions or just remove it for now?
Missing GDScript function in pair (plus_file - ===> path_join <===)
However is not valid. I am using path_join() right now in a beta4 project.

Of note I followed the directions that the Static Checks produces and attempted to do a git commit --amend. That does not work. So how would you like to proceed to fix my git history? Sorry I am not a git master. I know just enough to be dangerous.

If need be I can close this PR and create a fresh one with the changes that I have made, just let me know.

[Calinou]

Of note I followed the directions that the Static Checks produces and attempted to do a git commit --amend. That does not work.

Since you have more than 1 commit in your branch, you need to perform a rebase instead of amending your latest commit.

[FeralBytes]

Thanks @Calinou. I believe that should fix the git history.

[FeralBytes]

This PR: #69712 will result in my PR needing a change too.

[Riteo]

@FeralBytes it has already been merged BTW, you can already update your PR if that's what you're wondering.

[YuriSizov]

Needs to be rebased, but also will have to wait for the time after 4.0 (can probably be merged in 4.0.x, definitely in 4.1, if approved).

[FeralBytes]

It is stale now and has conflicts. Closing.