Tech Debt: Convert USWDS grid classes to CSS Grid

[levinmr]

Use CSS grid which has been supported natively in all browsers since 2017. Caveat: This will cause IE11 and older to not display the site grid properly (According to DAP stats, this is .1% of users to all govt sites).

This will reduce complexity in the site markup, keep positioning logic in the site CSS instead of HTML, and remove a unnecessary dependency on USWDS for positioning.

Documentation: https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_grid_layout