[Page updates] Pedestrian path to fix Google place routing

After various discussions on Discord over months, I made some changes to the pedestrian path, airport and places pages to document use of a routable pedestrian path to fix problems with external places. Specifically, I added problematic Google area place as a use case for routable paths, a link to routable path at the end of the airport page, and this subsection under the external providers section:

Enough people have asked about it, and enough editors have successfully used it for years, so I figured it should be documented somewhere. Let me know what you think.