Fixes WinToast failing to find the shortcut to check its AUMI because:
1) the app name given to WinToast did not match the shortcut name, and
2) it wasn't looking in the system-wide Start Menu.
Further, adds an option to fail if shortcut isn't found, rather than create it, because:
a) the shortcut would be to the WDBA, which is not useful, and anyway
b) we're showing the notification immediately after initializing WinToast, which
is too soon for Windows to reliably pick up on it, so it usually doesn't have the
desired effect of allowing the custom abstract model.
Differential Revision: https://phabricator.services.mozilla.com/D98838
Adam Gashlin