Extract ScriptInstance to simplify includes

This allows to include script_instance.h directly in the
generated gdvirtual.gen.inc, and remove excessive includes
from the codebase.

This should also allow Resource to use GDVIRTUAL macros,
which wasn't possible previously due to a circular dependency.

editor/plugins/animation_blend_tree_editor_plugin.h

@@ -31,6 +31,7 @@
 #ifndef ANIMATION_BLEND_TREE_EDITOR_PLUGIN_H
 #define ANIMATION_BLEND_TREE_EDITOR_PLUGIN_H
 
+#include "core/object/script_language.h"
 #include "editor/plugins/animation_tree_editor_plugin.h"
 #include "scene/animation/animation_blend_tree.h"
 #include "scene/gui/button.h"

editor/plugins/editor_preview_plugins.cpp

@@ -33,6 +33,7 @@
 #include "core/config/project_settings.h"
 #include "core/io/file_access_memory.h"
 #include "core/io/resource_loader.h"
+#include "core/object/script_language.h"
 #include "core/os/os.h"
 #include "editor/editor_paths.h"
 #include "editor/editor_scale.h"

editor/plugins/editor_resource_conversion_plugin.h

@@ -33,7 +33,6 @@
 
 #include "core/io/resource.h"
 #include "core/object/gdvirtual.gen.inc"
-#include "core/object/script_language.h"
 
 class EditorResourceConversionPlugin : public RefCounted {
 	GDCLASS(EditorResourceConversionPlugin, RefCounted);

editor/plugins/editor_resource_tooltip_plugins.h

@@ -33,7 +33,6 @@
 
 #include "core/object/gdvirtual.gen.inc"
 #include "core/object/ref_counted.h"
-#include "core/object/script_language.h"
 #include <scene/gui/control.h>
 
 class Control;

editor/plugins/packed_scene_translation_parser_plugin.cpp

@@ -31,6 +31,7 @@
 #include "packed_scene_translation_parser_plugin.h"
 
 #include "core/io/resource_loader.h"
+#include "core/object/script_language.h"
 #include "scene/gui/option_button.h"
 #include "scene/resources/packed_scene.h"
 

editor/plugins/script_editor_plugin.h

@@ -31,6 +31,7 @@
 #ifndef SCRIPT_EDITOR_PLUGIN_H
 #define SCRIPT_EDITOR_PLUGIN_H
 
+#include "core/object/script_language.h"
 #include "editor/editor_plugin.h"
 #include "scene/gui/dialogs.h"
 #include "scene/gui/panel_container.h"