Shortcut helper now shows correct application launch shortcuts.

Prior to this change, shortcut helper would build a list of application
launch shortuts based on the content of aosp bookmarks.xml. This list
would then be incorrect on devices with their own version of the file.

With this change, we request the shortcuts from system server after it
has parsed bookmarks.xml, so the set of shortcuts is complete and
correct.

Bug: 312452252
Flag: com.android.systemui.fetch_bookmarks_xml_keyboard_shortcuts
Test: atest KeyboardShortcutsTest KeyboardShortcutListSearchTest ModifierShortcutManagerTests ModifierShortcutTests
Change-Id: I4a3d34f93b0be12e5c48f5f8b3938c3e9f1618de