feat: upgrade to USWDS 3.9.0

[mdmower-csnw]

This pull request builds off of the work in #3263. When that pull request is merged, this will be rebased and moved out of draft status.

Summary

Apply updates related to features and bug fixes released by USWDS in 3.9.0.

• Apply usa-input--error to character count input on validation failure
• Add underlines to pagination links (for this project's button variants to align with the updated styles of anchors)
• Remove default assistive hint from combo box
• Do not trigger date picker on button click if component is aria-disabled true/"true"
  • Also auto-apply readonly to external input if not set via passed props
• Change nesting of Site Alert: Alert With Multiple Child Content to avoid excessive line breaks while still maintaining multiple children.
• Add autoComplete="email" prop to email inputs in stories
• Align unstyled modal buttons in stories... again.
• Removed numeric representation of months in the date of birth story, see USWDS - Memorable Date: Remove numbers from the dropdown list of months uswds/uswds#6028.

Related Issues or PRs

(none)

How To Test

Confirm things work the same as described in USWDS release notes: 3.9.0.

Happo differences

• Components/Button/Unstyled: Width of unstyled buttons changed for narrow screen widths in USWDS - Button: Collapse unstyled button width at small viewport sizes uswds/uswds#5631.
• Components/Pagination/*: Underlines added, see USWDS - Pagination: Updated text-decoration value to better show pagination links uswds/uswds#5970.
• Components/Character­Count/*: Red border around input when character count limit is exceeded is expected, see USWDS - Character count: Enhance visual cue when limit is exceeded uswds/uswds#5908.
• Components/Header/*, Page Templates/*: The slight shift in heading content is due to changed padding on usa-nav in USWDS - Header: Search input appears last in menu for mobile header. uswds/uswds#6037.
• Many alert changes: all a result of alignment updates in USWDS - Alert and Site alert: Adjust left alignment calculations uswds/uswds#5636 . From the USWDS release notes:

  Fixed a bug that caused $theme-site-margins-width to unexpectedly adjust the alignment inside the alert and site alert components. Alignment on the alert and site alert components will likely shift from this change. Confirm that your implementation of the component aligns as expected.