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.

core/extension/extension_api_dump.h

@@ -28,8 +28,8 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
-#ifndef API_DUMP_H
-#define API_DUMP_H
+#ifndef EXTENSION_API_DUMP_H
+#define EXTENSION_API_DUMP_H
 
 #include "core/extension/native_extension.h"
 
@@ -42,4 +42,4 @@ public:
 };
 #endif
 
-#endif // API_DUMP_H
+#endif // EXTENSION_API_DUMP_H

core/extension/gdnative_interface.h

@@ -582,4 +582,4 @@ typedef GDNativeBool (*GDNativeInitializationFunction)(const GDNativeInterface *
 }
 #endif
 
-#endif
+#endif // GDNATIVE_INTERFACE_H

core/extension/native_extension.h

@@ -97,4 +97,4 @@ public:
 	virtual String get_resource_type(const String &p_path) const;
 };
 
-#endif // NATIVEEXTENSION_H
+#endif // NATIVE_EXTENSION_H

core/extension/native_extension_manager.h

@@ -71,4 +71,4 @@ public:
 
 VARIANT_ENUM_CAST(NativeExtensionManager::LoadStatus)
 
-#endif // NATIVEEXTENSIONMANAGER_H
+#endif // NATIVE_EXTENSION_MANAGER_H