add loose autocomplete in Format type

[sebastianwd]

currently the type for the format parameter of the format function doesn't let typescript suggest the possible values. By using ({} & string) typescript shows the values while also alllowing any string as indended originally

before:

after:

[vercel]

@sebastianwd is attempting to deploy a commit to the Formkit Team on Vercel.

A member of the Team first needs to authorize it.

[justin-schroeder]

Thanks!