fix(#7375): fix dependency issues

[fgnass]

Summary

This PR addresses several dependency-related issues identified in #7375:

1. Turns slate-hyperscript from a dev dependency into a runtime dependency of decap-cms-widget-markdown
2. Updates clean-stack to v5.2.0 in decap-cms-core
3. Updates react-scroll-sync to v0.11.2 in decap-cms-core

This PR does not address the CSS import issue. Simply removing the imports would break the pre-build scripts, where these imports are resolved by webpack.

Test plan

Verified that the following issues are resolved:

• slate-hyperscript resolution error
• clean-stack browser compatibility error (os is not defined)
• React 19 compatibility error with react-scroll-sync

Checklist

• I have read the contribution guidelines.

A picture of a cute animal

🐼

[fgnass]

Update: The PR now also addresses the CSS issue by using babel-plugin-inline-import to inline the CSS.
The plugin is currently only applied when building the ESM version, so we can collect some feedback. In the future, we could use it for both flavors and remove the css-loader from the webpack config.

[fgnass]

Update: I noticed that the ESM code generated by babel contains a lot of unnecessary transforms that are not required in an ESM environment. I therefore updated the babel config to only use the non-standard plugins.

[alexwilson]

Hey @martinjagodic - could you please re-review this PR? 🙏🙏🙏