Editor: Cleanup some includes dependencies

Removes some unnecessary includes from `editor_node.h`, and instead add
those where they're used.

Removes unnecessary `editor_node.h` includes in various editor classes.

Renames `dynamicfont` to `dynamic_font` in a couple files.

Misc cleanup while jumping through that rabbit hole.

editor/scene_tree_editor.cpp

@@ -38,6 +38,7 @@
 #include "editor/node_dock.h"
 #include "editor/plugins/animation_player_editor_plugin.h"
 #include "editor/plugins/canvas_item_editor_plugin.h"
+#include "editor/plugins/script_editor_plugin.h"
 #include "scene/gui/label.h"
 #include "scene/main/window.h"
 #include "scene/resources/packed_scene.h"