Move AppItem into AppListModel

For better unit testings.

The AppItem used to be write with AppListPage, which is a little bit
hard to test, by moving it into AppListModel, AppItem could be tested as
other methods in AppListModel.

Also add more test cases for TogglePermissionAppInfoPage and
TogglePermissionAppListPage.

Bug: 260660819
Test: Unit test
Test: Manually with Settings
Change-Id: I646add1434d435ca3a8dbf7b34f39a705bae8754