On the panics dashboard, saw this panic of `There must be at least one
selection` in `open_locations_in_multibuffer`. Only seems to have
happened once in the past month.

Fix is to include the pending selection. Since `selections.all()` cannot
provide anchor selections, added `selections.all_anchors()` which only
really does any work if there is a pending selection.

Also fixes a corner case in jump-to-definitions where if the definition
is `HoverLink::InlayHint` and the `compute_target_location` fails for
all definitions it could potentially also trigger this case (and return
`Navigated::Yes` instead of `Navigated::No`

Release Notes:

- N/A