Controls: allow unsetting optional strings

[OliverJAsh]

Is your feature request related to a problem? Please describe.

When a component has an optional string prop, a "Set string" button appears (code here).

However, the opposite is not true. If the component has an optional string prop which has already been populated, it's not possible to unset the string prop:

The "reset controls" button doesn't help because (1) it will reset other things too and (2) this won't have any affect if the component had an arg defined initially.

Describe the solution you'd like

I would suggest an "unset" button beside the text input.

Describe alternatives you've considered

No response

Are you able to assist to bring the feature to reality?

yes, I can

Additional context

No response