[chore] Replace sass with sass-embedded

[jhutchison-nava]

Ticket

n/a

Changes

Replaces sass with sass-embedded

Context for reviewers

• This is a stacked-PR on [chore] Bump storybook to v10 #442. (Don't merge this if that PR has not been merged)
  • Related to [chore] Update USWDS style import #441.
• In order to get the full speed boost of [chore] Update USWDS style import #441, sass-embedded is required.
• There should be no downstream changes of the outputted CSS.

Note: Related to styling libraries, it seems like the following are unused and can be safely uninstalled, but I didn't want to increase the scope of the PR

• postcss
• postcss-loader
• postcss-preset-env
• sass-loader

Testing

• Storybook and Next.js still run and build. No noticeable CSS changes