Get hot reloading working

[TokisanGames]

Description

Hot reloading plugins was implemented Godot 4.2, but it doesn't automatically work for Terrain3D. Libraries are copied and named ~library.dll so the original can be replaced. And it may indeed reload the library. However (some?) Terrain3D functionality doesn't get updated. Maybe there's a signal it needs to capture to reload the editor plugin script or something else.