Ensure all layers in Mapbox style have reach_id field

[ngottlieb]

In order to differentiate between the active river and other rivers, we need to be able to access reach_id on all reach-specific layers in the style.

For reach_segments this is covered by the id of the feature, so we're ok there.

As of now in the NWI Experiments style, we're missing reach_id in the following:

• reach-segment-labels
• reach-class

I think that's it, will update this issue if I find more or with related needs

[mojodna]

The underlying data layer for both of those is reach-segment-labels-8f6her (source) and reach_segment-labels (layer). There should be an id for each feature there. QGIS shows it as mvt_id, but I think that's a driver artifact and it's not visible in Mapbox Studio, so...

Can you check whether you can access it from JS? If not, let's include a reach_id property in addition to whatever it's doing now.