LG-6158: Use FullScreen component for modal component

[aduth]

Why: To reuse common accessibility behaviors, including inert background content, focus trap, autofocus, deactivation triggers (e.g. escape button).

Testing Instructions:

1. Set idv_api_enabled: "true" in local config/application.yml
2. Go to: http://localhost:3000/verify/v2/personal_key_confirm
3. Observe that input field has focus
4. Tab through content up to and including the end of content
5. Observe that focus loops back to beginning of content after end
6. Activate screen reader web rotor
7. Observe that the only content listed in web rotor is modal content

Extra credit: Test to confirm there are no regressions to document capture Acuant SDK full-screen dialog experience.

Follow-up items:

FullScreen onRequestClose behaviors should be wired up to return the user to the previous step on Escape keypress or on clicking the backdrop. This depends on proposed changes at #6219.

[nprimak]

Works as expected! Definitely some things in here I'd like to familiarize myself with more.

[aduth]

Follow-up items:

FullScreen onRequestClose behaviors should be wired up to return the user to the previous step on Escape keypress or on clicking the backdrop. This depends on proposed changes at #6219.

Since #6219 was merged, I rebased the branch and wired up the FullScreen onRequestClose to trigger toPreviousStep in 9a171f9 (spec in fde87d1). I don't think I'll implement it here, but maybe it could also be good to have a "click outside to close" behavior, closing the dialog if the user clicks on the modal backdrop.