This will allow the diagnostic popover to be displayed even if hovering
an invisible char.
Beyond that, it solves a rare `DiagnosticPopover` corner case:
* Supports moving the selection to a diagnostic when `GoToDiagnostic` is
done while hovering, based on `group_id`
* Provides Diagnostic values with `group_id: 0` providing information on
hover about invisible characters.
So, `GoToDiagnostic` would navigate to the very first error produced by
a language server. Really not a big deal of course.
Release Notes:
- N/A
Michael Sloan
2dec4c2c91