Add Informal Foot Path preset

[arch0345]

This PR adds an unsearchable preset for highway=footway + informal=yes. I repurposed the Informal Path preset with the exception of the mtb_scale fields.

Also added the informal field to moreFields in the Foot Path preset

[tordans]

I don't know which infrastructure I would tag as informal footpath vs. informal path. IMO the informal key was clear in the sense that it is a "desire path" (Google images).

Could you describe your goal, mapper-usecase and add some numbers on tags?

[arch0345]

My goal was to have existing features tagged with highway=footway + informal=yes be labeled as 'Informal' instead of just being labelled as a Foot Path. However, I didn't really take into account how this could cause confusion as to which preset to use for these types of paths. I can change this to an unsearchable preset to avoid this.

An overpass query shows that there are currently around 2K features tagged with this combination, which is significantly less than the 100K tagged with highway=path:

[tordans]

We could pull all those values from the main preset (with this {} syntax), right? Same for moreTags. This way both stay in sync.

[tordans]

Sorry, I see this was stuck in pending state. And now it's merged. Will send it anyways; maybe we will refactor some day.

[tyrasd]

totally makes sense! I can consolidate the preset fields

[tyrasd]

oh, at second glance, I think it's probably not a good idea in this case: the informal presets purposefully omit some fields (most notably the name field, but also others like gnis/feature_id-US), and show other fields by default (e.g. trail_visibility / smoothness) while hiding some under the "more fields" section (e.g. structure). This makes it kind of impossible to use the field-inheriting feature.