Add job progress icon to the app bar

This adds a progress indicator to the app bar showing total progress of
running jobs. It is not yet interactable.

Bug: 385840940
Test: atest -c 'DocumentsUIGoogleTests:com.android.documentsui.JobPanelControllerTest'
Flag: com.android.documentsui.flags.visual_signals_ro

Change-Id: I9d81a0f36500c2239b7c7007efb3b1aae98467eb