Port to 4.4

[GM637]

The addon is completely unusable in Godot 4.4, a lot of functions is missing, a lot of parse errors, and Icons not showing up if used as button icons.

[rsubtil]

Hi, this is not specific to version 4.4. This is a current limitation of Godot that requires to re-open the project on the first time the addon is installed. I've just confirmed on v4.4.dev7 that it works as intended once you reload the project.

Please confirm if everything works correctly after that.

[the-old-one]

I can confirm that it works fine in 4.4-beta1.

Unfortunately I'm still constantly getting the following error reported previously.