Go back to existing tab instead of opening new one if document already open

Selecting a document in the browse view _always_ opens a new tab with that document, even if the document was already opened before.
We should go back to an existing tab with the previously opened document if it's already there to avoid multiple open tabs on the same document.

### Steps to Reproduce

1. Go to the browse view
2. Create a new document `foo` - this opens a tab with the foo document
3. Go back to the browse view, ensuring that the `foo` document is still open
4. Open the `foo` document

After step 4 you'll have 2 tabs with the `foo` document. It would be better to have jumped back to the already open tab for it.

Start in the browse view's document-selection flow and reproduce the listed steps with a document named `foo`. Trace how opening a document creates or selects tabs, then verify that selecting an already-open document returns to its existing tab rather than creating a duplicate.

Written by the indexing model from the issue text.