Log the reason why a WorkspaceItemInfo was removed

In the past we've seen a WorkspaceItem disappeared from the workspace
but wasn't able to determine why it was removed. This CL includes the
reason why it was removed in the error log, which hopefully would help
us debugging similar issues in the future.

Bug: 231239260
Test: make
Change-Id: Iba3d57568c9b3e011a6b65b26f0d4170d42fe1a5