[4.3] Replace Godot deprecated functions

[feiyunw]

Image::create() is deprecated, thus it does not exist if Godot is built with the Scons option "deprecated=no".
It must be changed to Image::create_empty() for better compatibility.

FYI:
https://github.com/godotengine/godot/blob/4.3-stable/core/io/image.cpp#L3428

[TokisanGames]

Thanks for this. However, this function does not exist in 4.2 and we're not ready to discontinue support yet. So, this PR can either alias create_empty if building in 4.2 or this PR will sit for a while until we're ready to drop 4.2.

[feiyunw]

Another problem for "deprecated=no" is that Godot is replacing NavigationMeshGenerator with the next generation Navigation and NavMeshComponents.

  res://addons/terrain_3d/src/baker.gd:197 - Parse Error: Identifier "NavigationMeshGenerator" not declared in the current scope.
  res://addons/terrain_3d/src/baker.gd:207 - Parse Error: Identifier "NavigationMeshGenerator" not declared in the current scope.
  res://addons/terrain_3d/src/terrain_menu.gd:-1 - Compile Error: 
  res://addons/terrain_3d/src/ui.gd:-1 - Compile Error: 
  res://addons/terrain_3d/editor.gd:-1 - Compile Error: 
  modules\gdscript\gdscript.cpp:2936 - Failed to load script "res://addons/terrain_3d/editor.gd" with error "Compilation failed". (User)
  res://addons/terrain_3d/src/terrain_menu.gd:12 - Invalid call. Nonexistent function 'new' in base 'GDScript'.
  res://addons/terrain_3d/src/terrain_menu.gd:30 - Invalid assignment of property or key 'plugin' with value of type 'EditorPlugin (editor.gd)' on a base object of type 'Nil'.

A new commit was submitted.

FYI:
https://github.com/godotengine/godot/blob/4.3-stable/modules/navigation/register_types.cpp#L50

[TokisanGames]

Thank you!