[charts] Move radar from under development to preview

[alexfauquette]

Preview: https://deploy-preview-17418--material-ui-x.netlify.app/x/react-charts/radar/

[mui-bot]

Deploy preview: https://deploy-preview-17418--material-ui-x.netlify.app/

Updated pages:

• docs/data/charts/radar/radar.md

Generated by 🚫 dangerJS against 1ef0958

[codspeed-hq]

CodSpeed Performance Report

Merging #17418 will not alter performance

_{Comparing alexfauquette:radar-expe (1ef0958) with master (0bb364f)}

Summary

✅ 8 untouched benchmarks

[bernardobelchior]

The PR title seems to indicate that we're marking radar as experimental, but the code is removing the development warning. I suppose the PR title should be "Mark radar as stable"?

[alexfauquette]

The PR title seems to indicate that we're marking radar as experimental, but the code is removing the development warning. I suppose the PR title should be "Mark radar as stable"?

For me, phases are:

1. Under development: We add basics features that could lead to breaking changes
2. Experimental: The component is ready to be tested by users, and breaking changes are allowed if needed
3. Stable: No more breaking changes