Shortcut Helper - Close the helper on CLOSE_SYSTEM_DIALOGS broadcast

The flag was already set to finishOnCloseSystemDialogs in the
AndroidManifest, but wasn't working.

The new approach is to manually register a broadcast receiver.

Flag: com.android.systemui.keyboard_shortcut_helper_rewrite
Test: Manual
Test: ShortcutHelperViewModelTest
Fixes: 343914445
Change-Id: I9751f37c70776cdafd123a416756c5954cb7e93b