Add a new special app access screen for long background tasks.

This new screen shows apps that hold the new RUN_LONG_JOBS permission.

Also add a reference to this screen in an app's info page under the
"Advanced" section for apps that have requested this permission.

Bug: 255821578
Test: atest AppFilterRegistryTest
Test: make -j RunSettingsRoboTests \
ROBOTTEST_FILTER="LongBackgroundTasksDetailsTest|
LongBackgroundTasksDetailsPreferenceControllerTest"
Test: visually via the Settings page

Change-Id: Idc498e52d29abc6df757c35e8bc91f00de92ba4a