Add Rego Playground to "Share" menu

[anderseknert]

VS Code provides a "Share" menu that appears when right clicking anywhere in the editor. Similar to the "Copy vscode.dev" link, it'd be nice if we had a "Copy Rego Playground Link".

We could do this by having the menu item call the PG API's v1/share endpoint with the policy from the active editor and input from the closest input.json file, if one exists.