Add a new HashSet template

* Intended to replace RBSet in most cases.
* Optimized for iteration speed

modules/gdscript/gdscript_tokenizer.h

@@ -32,8 +32,8 @@
 #define GDSCRIPT_TOKENIZER_H
 
 #include "core/templates/hash_map.h"
+#include "core/templates/hash_set.h"
 #include "core/templates/list.h"
-#include "core/templates/rb_set.h"
 #include "core/templates/vector.h"
 #include "core/variant/variant.h"