Define standard event for navigating IDEs to view a file + line + column

[polina-c]

Currently the DevTools > Inspector does a lot of extra work to navigate to select a widget. We should instead dispatch an event with a file + line + column indicating IDEs should navigate to that location.

Flutter should dispatch that event directly rather than relying on IDEs listening for the dart:developer inspect event. DevTools should also dispatch the event to trigger code navigation in the IDE from all places where DevTools wants to trigger navigation in the IDE.

Peer issue in DevTools: https://github.com/flutter/devtools/issues/4326