preview tabs: Allow replacing preview tab when using code navigation (#10730)

This PR adds support for replacing the current preview tab when using
GoToDefinition. Previously a tab, that was navigated away from, was
converted into a permanent tab and the new tab was opened as preview.

Without `enable_preview_from_code_navigation`:


https://github.com/zed-industries/zed/assets/53836821/99840724-d6ff-4738-a9c4-ee71a0001634

With `enable_preview_from_code_navigation`:


https://github.com/zed-industries/zed/assets/53836821/8c60efcb-d597-40bf-b08b-13faf5a289b6

Note: In the future I would like to improve support for the navigation
history, because right now tabs that are not "normal" project items,
e.g. FindAllReferences cannot be reopened

Release Notes:

- Added support for replacing the current preview tab when using code
navigation (`enable_preview_from_code_navigation`)

crates/command_palette/src/command_palette.rs

@@ -477,7 +477,7 @@ mod tests {
         });
 
         workspace.update(cx, |workspace, cx| {
-            workspace.add_item_to_active_pane(Box::new(editor.clone()), cx);
+            workspace.add_item_to_active_pane(Box::new(editor.clone()), None, cx);
             editor.update(cx, |editor, cx| editor.focus(cx))
         });