Allow navigating back to multibuffers (#9334)

Fixes
https://github.com/orgs/zed-industries/projects/14/views/1?pane=issue&itemId=56263346

Fixes a state where Zed multi buffers were not reachable after going to
an excerpt inside it (with alt-enter).
I suspect, we will have to come back to multi buffer history and check
the way it behaves on inner excerpts clicking, but now this change seems
to restore the main thing: multi buffers not being shown in the history
at all.



Release Notes:

- Fixes "go backwards" not considering multibuffers in history