Add types to shortcut

[sarayourfriend]

Description

Add types to Shortcut and update type-refinements in the component.

How has this been tested?

Local typecheck.

Types of changes

Type updates.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR.

/cc @sirreal

[sirreal]

Why the change to use ReactNode?

That seems to work in my testing, but this should really conform to JSXElementConstrcutor.

    type JSXElementConstructor<P> =
        | ((props: P) => ReactElement | null)
        | (new (props: P) => Component<P, any>);

The FunctionComponent type also returns ReactElement | null. (JSX.Element just extends ReactElement, so JSX.Element | null is also good)

[sarayourfriend]

I thought ReactNode was preferable as a single type, I didn't realize what the exact interface functional components adhered to. I'll change this back to JSX.Element | null 👍

[sirreal]

This change concerns me a bit… we only expect to receive a string or object, but this protected against other values before and doesn't after this change.

How do you feel about reverting it?

[sarayourfriend]

I will becuase I cannot reproduce the reason I made this change to begin with 🤦‍♀️ There was some issue with refining the type down to an object with the two properties, but it's working now, go figure.

[sirreal]

This looks good but it needs a rebase.

[sarayourfriend]

I'll reopen this PR in a second.