Prepare 6.0.0 release

[aduth]

Formality to publish the current main branch to NPM as 6.0.0, needed as part of LG-4502 to use the new bordered checkbox input.

Changelog:

6.0.0

Breaking Changes

• USWDS is upgraded to the latest version, from v2.9.0 to v2.11.2.
  • The bordered and large styles of checkboxes and radio buttons have updated guidance to improve compatibility with the USWDS tile style. The classes usa-radio-bordered, usa-radio-large, usa-checkbox-bordered, and usa-checkbox-large have been removed. Instead, add usa-radio__input--bordered, usa-radio__input--tile, usa-checkbox__input-bordered, usa-checkbox__input--tile respectively as modifiers to the element with the class usa-radio__input or usa-checkbox__input.
• The Accordion component no longer includes a "Close" button. Remove any instances of <button class="usa-accordion__close-button"> in your project, or references to the accordionCloseButton exported member of the JavaScript package.

[aduth]

Visual regression failure is due to version text being shown and changed on the home page.