refactor(splitbutton): deprecate component

[mdt2]

Description

Deprecating splitbutton. Setup for the deprecation was completed in #2526

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

• Splitbutton shows deprecation message in the docs site
• Splitbutton shows in the deprecated section in storybook
• All splitbutton code has been removed from components/
• Deprecation has followed the deprecation guidelines

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. ✨

[github-actions]

🚀 Deployed on https://pr-2527--spectrum-css.netlify.app

[github-actions]

File metrics

Summary

Total size: 3.93 MB^*

🎉 No changes detected in any packages

* Size determined by adding together the size of the main file for all packages in the library.
* Results are not gzipped or minified.
* An ASCII character in UTF-8 is 8 bits or 1 byte.

[castastrophe]

One note about the link and then we can merge this!

[castastrophe]

I also validated no regressions in Pagination button-style