Create a thread for MediaDataManager.

loading bitmap takes a long time. This makes the background handler
stuck and unable to execute tile clicks. This CL creates a new thread
for MediaDataManager class that is reponsible for loading bitmap of UMO.

Bug: 301287566
Test: atest MediaDataManagerTest
Test: Manual check on device playing media.
Test: used perfetto to verify that loading bitmap runs on a separate thread.
Change-Id: Ie2207c06cb203a399450c1d4e84a0bef0b068c08