[Media TTT] Show a loading icon when a media transfer is in

progress.

Bug: 203800327
Fixes: 203800721
Test: `adb shell cmd statusbar media-ttt-chip-add Tablet
TRANSFER_INITIATED` shows text AND loading icon. No other chip states
show loading icon.
Test: atest MediaTttChipControllerTest

Change-Id: I31740695f41627814d0d72094c7f9c927bffa9d3