Add option to convert project from Project Manager

[KoBeWi]

Closes godotengine/godot-proposals#4801

This is rather bare-bones implementation. It just opens a new dialog with a warning and runs the converter in the background. But IMO it's still better than hiding this option behind CLI.

ezgif.com-gif-maker.mp4

[jgillich]

Useful feature, but the initial dialog is confusing, it's not clear what the difference between "OK" and "Perform Full Project Conversion" is.

[qarmin]

#64396 will add two optional arguments - maximum file size and maximum line length, so I think that would be add them also here to be able to easily configure converter.

Since progress is visible command line, maybe better is to run converter with headless argument to not show new Godot window.

[bend-n]

What if there is a visual progress bar too?

[Calinou]

What if there is a visual progress bar too?

Drawing the progress bar may be more trouble than it's worth, but I suppose the window title could be changed to indicate progress.

[KoBeWi]

I updated the first dialog:

[akien-mga]

Thanks!