Recommend footway tags for piers and public transport platforms

[quincylvania]

man_made=pier public_transport=platform railway=platform

Features with these tags are expected to be part of the pedestrian network, but without highway tags it is more difficult for routers (and iD's validation) to support them. iD should add highway=footway automatically and recommend upgrading features lacking this tag.

Example: once the user upgrades the tags on the adjoining train platforms, the disconnected highway error on this path would be resolved:

We should also think of other tags that work like this.

[quincylvania]

In 8ac6ede028f9dfaa968e7b5b9f307478c56d5257 I added the highway tag to the addTags property of the relevant presets. We should add a validation that recommends adding missing tags in the addTags property to fully close this issue.

I also and added styling for racetracks with a highway tag: