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/import_defaults_editor.h

@@ -32,6 +32,7 @@
 #define IMPORT_DEFAULTS_EDITOR_H
 
 #include "scene/gui/box_container.h"
+#include "scene/gui/button.h"
 #include "scene/gui/option_button.h"
 
 class ImportDefaultsEditorSettings;