A plugin can declare `[[contributes.menus]]` with `menu = "viewItem.context"` and `view = "<its view>"`. Right-clicking an item of that tree or list view lists the matching commands, each run with the item's key as argument; `when` sees `viewItem` (the key) and `viewItemKind` (the key up to its first `:`). Validation refuses the menu without `view`, with an undeclared or web view, `view` on another menu, and (new in API 1.2) a manifest whose engines.openidea still admits older IDEs.
Closes#1618
Co-authored-by: arnaud-ritti <[email protected]>