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/editor_paths.cpp

@@ -34,7 +34,7 @@
 #include "core/config/project_settings.h"
 #include "core/io/dir_access.h"
 #include "core/os/os.h"
-#include "main/main.h" // For `is_project_manager`.
+#include "main/main.h"
 
 EditorPaths *EditorPaths::singleton = nullptr;