Add FormSteps React component

[aduth]

Why: To manage common behaviors of form values aggregation and history of a linear, step-based form.

Screen Recording:

The included example is provided for demonstration only, and is not intended to be styled or representative of a final flow. The intent of these changes is to prepare an apparatus for step-based forms flow which accumulates a single payload object, and which can be revised by the user using their browser history.

[zachmargolis]

LGTM

[aduth]

Per the discussions at #3952 (comment) and #3952 (comment), I took another shot at extracting a general-purpose useHistoryParam in 8332920, and updated the FormSteps component to work from the value of the name parameter as the source of truth, finding the appropriate step from that name.

A couple notes:

• As a reasonable compromise on the topic of browser support raised in Add FormSteps React component #3952 (comment), I chose to implement a limited polyfill of the behavior we would expect from URLSearchParams#get to retrieve a parameter value
• I revised the implementation to assign the parameter to the URL hash fragment instead of the URL query string. This was partly to facilitate testing (Error: Not implemented: navigation  jsdom/jsdom#2112), but generally speaking I think it's more common to see pushState used to modify hash fragments than it is to see them used to modify query parameters, so it could be an improvement all the same

[aduth]

Updated screen recording, since a few other pull requests have complemented the effort here toward a more realistic submission experience: