Fix dangling pointer crash in AppShortcutShelfItemController

This crash is caused by RegisterBrowserDidClose happening between
the browser's OnWindowClosing and BrowserList::RemoveBrowser.

The problem: AppShortcutShelfItemController constructor calls
ForEachCurrentBrowserWindowInterfaceOrderedByActivation() during the
timing window, which iterates BrowserList and stores raw_ptr to
browsers marked for deletion in browser_close_subscriptions_ map.
When these browsers are later destroyed, the raw_ptr keys become
dangling pointers, triggering partition_alloc detection.

Solution: Add is_delete_scheduled() checks in browser iteration
functions to skip browsers already marked for deletion, preventing
subscription to dying browsers.

Fixed files:
- browser_window_interface_iterator_non_android.cc: Added checks

      ran 100 times locally with all successes.

Bug: chromium:448384940
Test: ChromeOSWebAppExperimentsBrowserTest.LinkCaptureScopeExtension
Change-Id: I3ecee76b7ab87fa5a3379d59537d3e74be6dc238
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7014089
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Qikai Zhong <qikaizhong@microsoft.com>
Reviewed-by: Tom Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1526796}