Make core/ includes absolute, remove subfolders from include path

This allows more consistency in the manner we include core headers,
where previously there would be a mix of absolute, relative and
include path-dependent includes.

editor/editor_profiler.cpp

@@ -30,9 +30,9 @@
 
 #include "editor_profiler.h"
 
+#include "core/os/os.h"
 #include "editor_scale.h"
 #include "editor_settings.h"
-#include "os/os.h"
 
 void EditorProfiler::_make_metric_ptrs(Metric &m) {