Allow extensions to build custom UIs in the secondary side bar

[yaoleo34]

Currently, VS Code extensions can build its own UI on the primary side bar. Users can then move that UI to the secondary sidebar if they like. However, there is no VS Code APIs that allow extension developers to move UIs from primary to secondary side bar using code, and cannot add custom UIs in the secondary side bar.

We would like the following features:

1. Add the ability for extensions developers to move their extension's UI from the primary side bar to the secondary side bar
2. Add the ability for extension developers to create custom UI in the secondary side bar, similar to the primary side bar.

[iwangbowen]

We need new APIs

[vs-code-engineering]

Thanks for creating this issue! We figured it's covering the same as another one we already have. Thus, we closed this one as a duplicate. You can search for similar existing issues. See also our issue reporting guidelines.

Happy Coding!

[JerryYangKai]

I have tried this contribute code, but it seems not support add a tool view in secondary side bar. It turns out an error 'no data provider'.
#247899