Migrate breakpoint names for flex utility classes

[jamigibbs]

Note: Delete the description statements, complete each step. None are optional, but can be justified as to why they cannot be completed as written. Provide known gaps to testing that may raise the risk of merging to production.

Summary

This PR will migrate the breakpoint names for the flex utility classes.

Current VADS Name	USWDS v3 Name
xsmall-screen (320px)	mobile (320px)
small-screen (480px)	mobile-lg (480px)
small-desktop-screen (1008px)	desktop (1024px)
large-screen (1200px)	desktop-lg (1200px)

Related issue(s)

• CSS Library - Utilities - Swap flexbox import vets-design-system-documentation#3208

Testing done

• confirmed locally that the new breakpoint names were applying from the CSS Library utilities stylesheet on a drupal liquid page (home page)

Screenshots

Note: This field is mandatory for UI changes (non-component work should NOT have screenshots).

	Before	After
Mobile
Desktop

What areas of the site does it impact?

(Describe what parts of the site are impacted if code touched other areas)

Acceptance criteria

Quality Assurance & Testing

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Linting warnings have been addressed
• Documentation has been updated (link to documentation *if necessary)
• Screenshot of the developed feature is added
• Accessibility testing has been performed

Error Handling

• Browser console contains no warnings or errors.
• Events are being sent to the appropriate logging solution
• Feature/bug has a monitor built into Datadog or Grafana (if applicable)

Authentication

• Did you login to a local build and verify all authenticated routes work as expected with a test user

Requested Feedback

(OPTIONAL) What should the reviewers know in addition to the above. Is there anything specific you wish the reviewer to assist with. Do you have any concerns with this PR, why?

[eselkin]

LGTM. I have a PR with pretty much the same changes for facility pages.