Refactor Object metadata

* API kept the same (Although functions could be renamed to set_metadata/get_metadata in a later PR), so not much should change.
* Metadata now exposed as individual properties.
* Properties are editable in inspector (unless metadata name begins with _) under the metadata/ namespace.
* Added the ability to Add/Remove metadata properties to the inspector.

This is a functionality that was requested very often, that makes metadata work a bit more similar to custom properties in Blender.

tests/core/object/test_object.h

@@ -133,7 +133,7 @@ TEST_CASE("[Object] Core getters") {
 }
 
 TEST_CASE("[Object] Metadata") {
-	const String meta_path = "hello/world complex métadata\n\n\t\tpath";
+	const String meta_path = "complex_metadata_path";
 	Object object;
 
 	object.set_meta(meta_path, Color(0, 1, 0));