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.

modules/gdscript/gdscript_parser.h

@@ -31,11 +31,11 @@
 #ifndef GDSCRIPT_PARSER_H
 #define GDSCRIPT_PARSER_H
 
+#include "core/map.h"
+#include "core/object.h"
+#include "core/script_language.h"
 #include "gdscript_functions.h"
 #include "gdscript_tokenizer.h"
-#include "map.h"
-#include "object.h"
-#include "script_language.h"
 
 struct GDScriptDataType;
 struct GDScriptWarning;