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/plugins/input_event_editor_plugin.h

@@ -33,8 +33,7 @@
 
 #include "editor/action_map_editor.h"
 #include "editor/editor_inspector.h"
-
-class EditorNode;
+#include "editor/editor_plugin.h"
 
 class InputEventConfigContainer : public HBoxContainer {
 	GDCLASS(InputEventConfigContainer, HBoxContainer);