Rearrange collab titlebar items to avoid movement of the toggle contacts button

* Replace username in titelbar with a `...` user menu that shows
  the current user name and contains a sign-in/sign-out button.
* Move the '+' (toggle contacts) button back to the right side.
* Move the collaborators back to the right side.
* Move the share/unshare button to the left side, beside the project title
* Only show the share/unshare button when in a call.

styles/src/styleTree/workspace.ts

@@ -197,6 +197,11 @@ export default function workspace(colorScheme: ColorScheme) {
           color: foreground(layer, "variant", "hovered"),
         },
       },
+      userMenuButton: {
+        buttonWidth: 20,
+        iconWidth: 12,
+        ...titlebarButton,
+      },
       toggleContactsBadge: {
         cornerRadius: 3,
         padding: 2,