With the assumption that IDEs will not create a debug session for the
widget previewer, the widget inspector's source navigation functionality
won't function as there's no IDE to listen to `navigate` events sent via
`postEvent`.
This change overrides some widget inspector behavior to allow for
navigating to source locations via the DTD Editor service instead of
relying on the VM service's `postEvent`.
This change also makes some minor changes to the diagnostic properties
and descriptions displayed within the inspector to display group and
custom preview annotation details.
Towards https://github.com/flutter/flutter/issues/166423
37487b3e4c