[1/n] Adding tiling session persistence to the repositories

This CL adds the persistence data to persistent_desktop_repositories.proto
and introduces the means to read and write this field through
DesktopRepositories and DesktopPersistenceRepository.

This CL does NOT initialize tiling upon device reboot and just persists the
tiling data.
The actual initialization will come at a later CL.

Flag: com.android.window.flags.enable_tile_resizing

Test: unit tests

Bug: 400973989

Change-Id: Ibd4cc1115cbe6f4ac055f033a2a9987d92470e23