feat!: 🎉 Spectrum 2 foundations

[pfulton]

Description

This pull request brings in the Spectrum 2 design foundations tokens to start the migration from our current design system to the latest. To accommodate these changes, this pull request makes a few updates to our build to facilitate more robust theme switching.

How and where has this been tested?

Please tag yourself on the tests you've marked complete to confirm the tests have been run by someone other than the author.

Remaining TODOs

• Need a decision about how we're going to handle the QuickAction deprecation in the Card documentation
• Resolve the remaining S1 & Express VRTs
• Write out additional tests cases for the postcss-splitinator plugin to cover the expanded pseudo and combinator support
• Storybook: clean up theme switching to load only the required assets per context and check for bugs or regressions
• After the modes branch is merged, resolve conflicts in rebase and add new context mode; check vrt baselines for regressions in express and legacy

Validation steps

Validating the compiled output

• Expect to see only the 1 top-level class .spectrum--express in the dist/themes/express file; this class should contain --system prefixed variables
• Expect to see only the 1 top-level class .spectrum--legacy in the dist/themes/legacy.css file; this class should contain --system prefixed variables
• Expect to see only the 1 top-level class .spectrum in the dist/themes/spectrum.css file; this class should contain --system prefixed variables
• Expect to see the component class names in the dist/index-theme.css file but no top-level classes (i.e., no .spectrum or .spectrum--legacy)

Validating the compiled token output

• Expect to see a tokens/components and tokens/dist/css/components folder with bridge, express, legacy, and spectrum folders inside
• Expect the tokens/components/bridge/actionbutton.css file to match the components/actionbutton/dist/index-theme.css output
• Expect the tokens/components/spectrum/actionbutton.css file to match the components/actionbutton/dist/themes/spectrum.css output
• Expect the tokens/components/legacy/actionbutton.css file to match the components/actionbutton/dist/themes/legacy.css output
• Expect the tokens/components/express/actionbutton.css file to match the components/actionbutton/dist/themes/express.css output

Regression testing

Validate:

1. The documentation pages for at least two other components are still loading, including:

• The pages render correctly, are accessible, and are responsive.

2. If components have been modified, VRTs have been run on this branch:

• VRTs have been run and looked at.
• Any VRT changes have been accepted (by reviewer and/or PR author), or there are no changes.

Screenshots

To-do list

• I have read the contribution guidelines.
• I have updated relevant storybook stories and templates.
• I have tested these changes in Windows High Contrast mode.
• If my change impacts other components, I have tested to make sure they don't break.
• If my change impacts documentation, I have updated the documentation accordingly.
• ✨ This pull request is ready to merge. ✨