Only cache low-resolution task snapshots in the system server.(5/N)

This change reduces both heap and dma_buf usage in the system server by
replacing high-resolution snapshots in the cache with low-resolution:

1. After a low-resolution bitmap is created in the persist thread, a
new task snapshot object is created from it. This then replaces the
previous high-resolution snapshot in the snapshot cache.
2. When getTaskSnapshot is called with a low-resolution request, a
low-resolution snapshot is either retrieved or created from the latest
task snapshot (if it exists). This replaces the high-resolution
snapshot in the snapshot cache. By respect the request, this also
reduce the memory usage in the client process since the returned
snapshot is smaller than the high-resolution one.

To prevent duplicate tasks resulting from both scenarios (1 and 2),
the second put-to-cache task can be ignored if the convert already
occurred.

3. Support takeTaskSnapshot to return a low-resolution snapshot, which
will be useful when clients request a snapshot but specifically require
a lower-resolution version.

Flag: com.android.window.flags.reduce_task_snapshot_memory_usage
Flag: com.android.window.flags.respect_requested_task_snapshot_resolution
Bug: 238206323
Test: dumpsys window every time after a close task transition finish,
verify the resolution in task snapshot cache is low-resolution.
dump dmabuf everytime after a close task transition finish, verify the
dmabuf won't increase in system server.

Change-Id: I37ebbef4f75a86c952f8e633fdbc8aedaf5b3d69