At first I worried that we were missing code to clear `_matchers` when the context changes (e.g. the same Go to Definition query in different files yields totally different matches).  But then I realized the whole `QuickNavigateDialog` gets thrown out every time the bar is closed.  I wonder if it's worth noting that in the `_matchers` docs anywhere, to alleviate any confusion about when the state is cleared?  (Or perhaps in the extension-author-facing docs that explain the new matcher arg).