Code quality: Fix header guards consistency

Adds `header_guards.sh` bash script, used in CI to validate future
changes. Can be run locally to fix invalid header guards.

modules/gdscript/language_server/gdscript_extend_parser.h

@@ -33,7 +33,7 @@
 
 #include "../gdscript_parser.h"
 #include "core/variant/variant.h"
-#include "lsp.hpp"
+#include "godot_lsp.h"
 
 #ifndef LINE_NUMBER_TO_INDEX
 #define LINE_NUMBER_TO_INDEX(p_line) ((p_line)-1)
@@ -99,4 +99,4 @@ public:
 	Error parse(const String &p_code, const String &p_path);
 };
 
-#endif
+#endif // GDSCRIPT_EXTEND_PARSER_H