Device Page: support different distance units

[ybott-qinetic]

Contributes to #2846

[blammit]

Thinking about the renaming that we discussed yesterday, we can rename Units_Altitude_Metre to Units_Metre, and then that unit can be used regardless of whether we are measuring altitude or land distance. That will make sense for both /Units/Altitude and any potential future /Units/Distance. Same with Units_Altitude_Foot, it should be Units_Foot instead. Can you make this renaming change as a first (separate) commit in this PR?

[blammit]

When adding Units_Kilometre, update units.cpp to avoid scaling for this unit, so that it's not possible to scale to a number like "1.2 kkm".

Also can you add unit tests for the new units? See tst_units.qml.

I wasn't sure initially about adding Units_Kilometre if we already have Units_Metre - will it cause confusion about which one to use? But I suppose it's convenient to have both if you want to don't want to convert the source VeQuickItem value when displaying a "km" value in a QuantityLabel. And then we could also use it for direct unit conversions with VeQuickItem::sourceUnit.

[ybott-qinetic]

I think I have addressed the above items.

[blammit]

Instead of having _metresToSystemDistanceUnit(), you can do unit conversions directly on the data item, using VeQuickItem::sourceUnit and VeQuickItem::displayUnit. To do this, update the veutil unit conversions:

• Add Kilometre, Mile and NauticalMile alongside Metre and Foot
• Update the AltitudeConverter to do those new unit conversions

Then you can do the conversions directly on the data item and it will show the correct value:

ListQuantity {
    //% "Range"
    text: qsTrId("ev_range")
    dataItem.uid: root.bindPrefix + "/RangeToGo"
    dataItem.sourceUnit: Units.unitToVeUnit(VenusOS.Units_Kilometre)
    dataItem.displayUnit: Units.unitToVeUnit(_systemDistanceUnit())
    unit: root._systemDistanceUnit()
}

(See other uses of sourceUnit and displayUnit in gui-v2.)

[ybott-qinetic]

Done

[blammit]

Also, instead of "Device Page", use "EV" for the commit message subject (or "Units" for the unit-only commit) as this change does not generically apply to device pages in general.