Implement no-window mode for X11 and MacOS (3.2)

[RandomShaper]

This adds support for --no-window to MacOS and X11.

It also makes the non-windowed and non-overridden versions of OS::alert() include the title as well.

The credit for the MacOS support goes to a developer called Anton Breusov, on top of which I applied minimal changes. It seems that on Mac we can't get perfect hidden window behavior (it's still shown in the dock, though unpickable) and we need stronger measures to have it working as closer to expected as possible, as the code changes show.

NOTE: There's no version of this for 4.0, since, as far as I've checked, 4.0 still doesn't implement --no-window at all. Therefore, I believe that a good plan is that when it's implemented there the 3.2 version is more platform-complete so it gets everything at once.

Bugsquad edit: Fixes #43325.

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This code is generously donated by IMVU.

[capnm]

I think --no-window could be a default by --script.
In the other few cases, you could use the --window option.

[RandomShaper]

I think --no-window could be a default by --script.
In the other few cases, you could use the --window option.

That's a good idea, but I would leave 3.x as it is to avoid surprising changes. For 4.0 it's fine, I think.

[capnm]

That's a good idea, but I would leave 3.x as it is to avoid surprising changes. For 4.0 it's fine, I think.

For --gdnative-generate-json-api, etc. too.

I would keep it the same to avoid a chaos;)
You could probably print a warnig or let also the --no-window option for compatibility reasons?

FYI I've made it the default wherever it's been useful and added both options:

-	OS::get_singleton()->print("  --no-window                      Disable window creation (Windows only). Useful together with --script.\n");
+	OS::get_singleton()->print("  --window, --no-window            Run with or without opening a window. Useful with --script.\n");

[capnm]

Some notes:
Edit: sorry Godot seems to ignore unknown arguments;)

godot-32x --no-window -s test.gd runs a gdscript w/o window and keeps hanging...

Maybe the comment could mention that you need to explicitly call the quit() function.

-s, --script <script> Run a script.

[pouleyKetchoupp]

The X11 part looks fine and seems to work well.

[bruvzg]

Works OK on macOS, but App icon will appear in the Dock.

[akien-mga]

@RandomShaper See review comments from @bruvzg, once amended this should be good to go.

[akien-mga]

Thanks!

[Xrayez]

I think --no-window could be a default by --script.
In the other few cases, you could use the --window option.

That's a good idea, but I would leave 3.x as it is to avoid surprising changes. For 4.0 it's fine, I think.

There are definitely use cases where having a Window is necessary when running with --script, like for running unit tests. See also godotengine/godot-proposals#1760.

As far as I know, it's not just a "script" which is run by Godot, it's a MainLoop derived script which just overrides the main loop implementation.

This is just to be aware if you do decide to make it a default, adding another --windowed option would be absolutely necessary.