Needs to be updated for Godot 4.0

[Poonaka]

When trying to enable the plugin, I get a few errors:

Parse Error: Unexpected "Identifier" in class body

Turns out that the "tool" keyword now needs an @ symbol like "@tool". I tried updating that but now I am faced with some more errors:

res://addons/MagicaVoxelImporterwithExtensions/VoxFormat/VoxMaterial.gd:4 - Parse Error: Expected end of statement after variable declaration, found "Identifier" instead.
  res://addons/MagicaVoxelImporterwithExtensions/GreedyMeshGenerator.gd:104 - Parse Error: Cannot use subscript operator on a base of type "null".
  res://addons/MagicaVoxelImporterwithExtensions/GreedyMeshGenerator.gd:121 - Parse Error: Identifier "SpatialMaterial" not declared in the current scope.
  res://addons/MagicaVoxelImporterwithExtensions/GreedyMeshGenerator.gd:186 - Parse Error: Cannot find property "xform" on base "Basis".
  res://addons/MagicaVoxelImporterwithExtensions/GreedyMeshGenerator.gd:186 - Parse Error: Function "xform()" not found in base Basis.
  res://addons/MagicaVoxelImporterwithExtensions/vox-importer.gd:7 - Parse Error: Constant value uses script from "res://addons/MagicaVoxelImporterwithExtensions/VoxFormat/VoxMaterial.gd" which is loaded but not compiled.
  res://addons/MagicaVoxelImporterwithExtensions/vox-importer.gd:9 - Parse Error: Constant value uses script from "res://addons/MagicaVoxelImporterwithExtensions/GreedyMeshGenerator.gd" which is loaded but not compiled.
  res://addons/MagicaVoxelImporterwithExtensions/vox-importer.gd:76 - Parse Error: Function "PoolByteArray()" not found in base self.
  res://addons/MagicaVoxelImporterwithExtensions/vox-importer.gd:95 - Parse Error: Invalid argument for "save()" function: argument 1 should be Resource but is String.
  res://addons/MagicaVoxelImporterwithExtensions/vox-importer.gd:242 - Parse Error: Cannot find property "xform" on base "Basis".
  res://addons/MagicaVoxelImporterwithExtensions/vox-importer.gd:242 - Parse Error: Function "xform()" not found in base Basis.
  res://addons/MagicaVoxelImporterwithExtensions/plugin.gd:7 - Parse Error: Constant value uses script from "res://addons/MagicaVoxelImporterwithExtensions/vox-importer.gd" which is loaded but not compiled.
  Transient parent has another exclusive child.