Reapply "Handle queued state for progress messages"

This reverts commit 2b80b10b.

The tests added were testing behaviour gated behind the visual signals
flag, but the tests themselves were not gated. Duplicate the relevant
tests so that only test new functionality when the flag is on.

Bug: 407674989
Test: atest -c 'DocumentsUIGoogleTests:com.android.documentsui.services'
Flag: com.android.documentsui.flags.visual_signals_ro
Change-Id: I74f13929f6fba76a2b4d4cd40c3d4c16158692ce