windowManager: Expose WorkspaceTracker blockUpdates & unblockUpdates

windowManager: Expose WorkspaceTracker blockUpdates & unblockUpdates

Update blocking is currently only used by the workspace switcher popup,
but the workspace animation needs to do the same.

To prepare for that, expose block workspace updates on WindowManager
to make it available outside the module.

Use a counter to track block/unblock calls and avoid contention over the
_pauseWorkspaceCheck boolean inside WorkspaceTracker.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/4014>
(cherry picked from commit 217b1502057a78b13a3a5dd73a8b202e81aec127)