feat: multi-project workspaces and project window groups (#448)

Workspaces open several local project folders in one IDE session (File › New / Open / Manage Workspace…, or Attach when opening a project, which creates a workspace automatically for a plain project window). Member folders are the Project view roots and take part in indexing, Find in Files, Git, language servers, run configurations and builds; agent tasks choose which member they work in. Window › Merge All Project Windows groups project windows into one window with project tabs (switch, reorder, close, move to a new window), restored on reopen.

Closes #241
Closes #198
Closes #286

src/platform/keymaps/intellij-macos.ts

@@ -186,6 +186,8 @@ export const intellijMacos: Record<string, string[]> = {
   "editor.nextSplitter": ["Alt+Tab"],
   "editor.prevSplitter": ["Alt+Shift+Tab"],
   "window.toggleFullScreen": ["Meta+Ctrl+F"],
+  "window.nextTab": ["Meta+Alt+PageDown"],
+  "window.previousTab": ["Meta+Alt+PageUp"],
   "window.next": ["Meta+Alt+`"],
   "window.previous": ["Meta+Alt+Shift+`"],
   "file.reloadFromDisk": ["Meta+Alt+Y"],

src/platform/keymaps/intellij-windows.ts

@@ -187,6 +187,8 @@ export const intellijWindows: Record<string, string[]> = {
   "editor.nextSplitter": ["Alt+Tab"],
   "editor.prevSplitter": ["Alt+Shift+Tab"],
   "window.toggleFullScreen": [],
+  "window.nextTab": ["Ctrl+Alt+PageDown"],
+  "window.previousTab": ["Ctrl+Alt+PageUp"],
   "window.next": ["Ctrl+Alt+]"],
   "window.previous": ["Ctrl+Alt+["],
   "file.reloadFromDisk": ["Ctrl+Alt+Y"],