[Feature] continuous visualmap also show range and text

[coader]

What problem does this feature solve?

now only a bar without range, if use piecewise, it show several stacked bar

What does the proposed API look like?

[github-actions[bot]]

This issue has been automatically marked as stale because it did not have recent activity. It will be closed in 7 days if no further activity occurs. If you wish not to mark it as stale, please leave a comment in this issue.

[github-actions[bot]]

This issue has been automatically closed because it did not have recent activity. If this remains to be a problem with the latest version of Apache ECharts, please open a new issue and link this to it. Thanks!