Fix compilation errors for Godot 4.2

[SaracenOne]

Implements the missing abstract functions to allow the module to be compiled for Godot 4.2.

[fire]

Probably need to add to our documentation to rename the module to “visual_script” from “godot_visual_script”. Or rename our fork.

[SaracenOne]

I'll put it back to the old name for now.