Start a new mode to draw area polygons snapped to roads! https://gith…

[dabreegster]

…ub.com/acteng/atip/issues/118

screencast.mp4

Here's a working area drawing tool that snaps to roads! It's a bit clunky, but I'm happy with it as a v1. I'll followup with a PR in ATIP to integrate it.

Some of the unsolved bugs / design warts:

• No attempt to "backfill" or import an existing polygon produced in another tool. You can edit a polygon made with this tool only.
• No freehand points at all in this mode. We can relax this constraint later, but it gets tricky. For now, I'm picturing two separate polygon tools in ATIP -- the current freehand one and this one. Won't be able to mix and match yet.
• You can delete waypoints by clicking them, unless it happens to be the first waypoint, which is a bit special internally.
• Sometimes a waypoint winds up looking like a linear route that doubles back on itself; the resulting polygon is a bit broken. The user can visually avoid this; it's obvious when it goes wrong.
• After drawing a closed polygon, I've sometimes clicked and managed to incorrectly insert a new waypoint at the very end, creating a linestring that escapes the polygon. This is incorrect / a bug. I can't repro yet; I'll click more carefully in future tests. :)

CC @robinlovelace-ate and @Sparrow0hawk. Async code review always welcome

[robinlovelace-ate]

This is absolutely amazing 🤯

Will be useful for designing areal interventions in Design mode, in addition to planning. Great work Dustin 👏 🎉 🎉