USWDS-Site - Layout grid: Mixin guidance doesn't match other utilities

[mahoneycm]

Is your feature request related to a problem? Please describe.

The layout grid mixin guidance does not follow patterns set by other utility classes and generally could be improved.

Describe the solution you'd like

Convert to mixin table similar to flex utility mixin guidance.

Describe alternatives you've considered

No response

Additional context

Screenshots

Layout grid

Display flex

Code of Conduct

• [X] I agree to follow this project's Code of Conduct.
• [X] I checked the current issues for duplicate feature requests.