feat(window): close other / left / right project tabs from the window-group tab menu (#965)

Right-clicking a project tab in a merged window group offers Close Other Tabs, Close Tabs to the Left and Close Tabs to the Right (left/right disabled at the ends); the same commands are in the Command Palette and can take shortcuts.

The backend closes the projects one at a time, focusing each so its own unsaved-changes prompt is visible, as Quit does. Cancelling a prompt stops the batch and leaves that project and the rest open; the clicked tab stays and is selected when the batch finishes. Starting Quit clears a pending batch.

Closes #942.

Co-authored-by: jaw52 <[email protected]>

src/platform/locales/text/zh.json

@@ -5008,6 +5008,9 @@
   "Window group": "窗口组",
   "Select Project Tab": "选择项目标签页",
   "Close Project Tab": "关闭项目标签页",
+  "Close Other Project Tabs": "关闭其他项目标签页",
+  "Close Project Tabs to the Left": "关闭左侧项目标签页",
+  "Close Project Tabs to the Right": "关闭右侧项目标签页",
   "Reorder Project Tabs": "重新排列项目标签页",
   "Close {name}": "关闭 {name}",
   "Tomcat Server": "Tomcat 服务器",