Confusing add_theme_override functions name parameter

**Your Godot version:**
4.5

**Issue description:**
The `name` parameter in all `add_theme_[something]_override` is not properly explained and users may have a very difficult time using those functions because of it. I had to find this topic to be able to use `add_theme_font_override` :

https://forum.godotengine.org/t/godot-4-font-size-does-not-change-when-set-by-code/569/2

I still don't understand how it works though. If a theoretical explaination of what `name` means in this context isn't appropriate, I suggest to include one example :

`add_theme_font_size_override("font_size", font_size)`

So that users can make the function work without having to dig up the forum thread.

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/4.4/classes/class_control.html#class-control-method-add-theme-font-override