mini-widget: display rangefinder altitude

[ES-Alexander]

Problem to solve

It is common for subs and boats to use echosounders as altimiters.

This information is valuable for many of our users, and seems worth having a convenient pre-made interface for, rather than needing to configure a custom VGI (which adds friction and support/documentation load).

Desired approach

There are a few main options:

1. Create a dedicated rangefinder mini-widget
   • This takes some work, but could be used for an obstacle indicator just as easily as an altitude (or depth) indicator
   • Could use the reported sensor orientation to set an appropriate icon automatically
2. Add a rangefinder option to the VGI presets
   • This is likely very easy to do, but is potentially a little redundant
   • It has similar generality to a dedicated mini-widget, but the user would need to change the icon if they want it direction dependent
3. Add rangefinder as a selectable depth/altitude input source, for use in the existing depth and altitude mini-widgets
   • This is somewhat limited in output potential, but also fits nicely into existing widgets instead of duplicating them
   • Data source selection is a more general thing we're working on with Cockpit, and this could join those efforts

Additional context

247 provides a longer term interface design goal for this, with integration into the main depth/altitude widget. That said, we don't have a timeline for when that will be completed, so adding a convenient mini-widget option in the interim still seems worthwhile.

Raised by G / @vshie / @dgudiel

Prerequisites

• [X] I have checked to make sure that a similar request has not already been filed or fixed.