🗨️ Enhancements to `Commenting`

[echarles]

Follow-up further to datalayer/vscode-datalayer#124 (comment)

1. Some buttons are not aligned properly
2. Use native modal dialog for deleting comments? or style to better match the look and center on the whole window?
3. Use native input dialog for introducing comments?
4. Simplify look and style of the comment sidebar. Looks a bit crowded.
5. if the comment panel is hidden and one moves the cursor over a commented line, it will open the sidebar automatically, might not be the desired behavior.
6. Do we want to add Accept Comment button... to mark it as handled... without having to delete it or something?