Add highway=corridor and crossing=*, sidewalk=* tags for roads layer

[nvkelso]

New roads layer features:

• highway=corridor - starting at zoom 16, to support indoor mapping and layering on top of buildings. Example in SFO, read more on OSM wiki

New attributes on roads layer features:

• crossing=* - starting at zoom 17, to support pedestrian mapping. Example in NYC, read more on OSM wiki. Drop this attribute at earlier zooms.
• sidewalk=* - starting at zoom 15, to support pedestrian mapping. Example in SF, read more on OSM wiki. Drop this attribute at earlier zooms.

[rmarianski]

It looks like elements can have crossing and sidewalk keys, as well as having footway values. Do we want to normalize these somehow?

I originally read the issue as passing the truthy crossing and sidewalk tags through to the tile properties, but the nyc example only has footway=crossing and no crossing tag.

[nvkelso]

We added some footway=* (mostly sidewalk and crossing) in v0.10 release. Let's take this opportunity to normalize (whitelist) values and share that whitelist with crossing=* and sidewalk*=* values.

[nvkelso]

Corridors are coming thru, but we might want to set their default sort order above buildings?

I've adjusted them above in the screenshot below:
18/37.61770/-122.38177

[nvkelso]

For sidewalk (which are now coming thru!), it looks like the vast majority of values (850,000) are in the primary sidewalk key, but there are optional sidewalk:left and sidewalk:right tags listed in TagInfo, like we support for bicycle lanes, but both those side variants have less than 1000 uses. But it seems like for complete streets inventories the gaps are important and we should also pass them thru.