feat(dropshadows): adds dropshadows to commons

[jenndiaz]

Description

Adds S2 Drop Shadow styling to commons
Allowing for dropshadows to be imported @import "../commons/dropshadows.css"; and used with in classes @inherit: %spectrum-DropShadow-key;

TO DO:

• update with S2 tokens once they are released

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.

Validation steps

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. ✨

[castastrophe]

Would it be valuable to split out the variable definitions from the css property definitions? Just trying to think of examples where someone might want to variables and properties to source from different levels (properties at root for example).

[castastrophe]

I think these might be added from an old version. We don't use npm-run-all or concat-cli anymore for token building.

[castastrophe]

Just a note for future to use @import "@spectrum-css/commons/dropshadows.css" instead and document that the commons package needs to be added as a devDependency.

[jawinn]

This was great exploratory work, thanks Jenn!
The followup PR that finalizes the drop shadow foundations info is #2674 (merging soon into spectrum-two).