Use dictionary for passing in props (strings are still allowed for backwards compatibility and short-hand notation)

[evnchn]

With reference to #4453

In props.py class Prop:, Instead of accepting a string (add: Optional[str] = None), would it be better to accept either a string for backwards compatibility and short-hand notation, while also accepting a dictionary (hypothetically speaking: add: Optional[Union[str, Dict[str, Union[str, int, float, bool]]]] = None)?