Issue Type: Feature Request

Testing #93819

1. Open a timeline from a file in the explorer
   -> timeline is pinned to that file
2. keep working: open editors, browse etc.
   -> At some point you forget that you pinned the timeline and looking at the history becomes a puzzler as the history does not make sense, then you realize the different file name but you still don't see it's locked. You have to go to explicitly hover over the view titlebar to see the "unpin" icon

VS Code version: Code - Insiders 1.44.0-insider (d7d1147, 2020-03-31T08:22:34.682Z)
OS version: Darwin x64 18.7.0
Remote OS version: Linux x64 5.0.0-1022-azure
Remote OS version: Linux x64 5.0.0-1022-azure