Internal Rust cleanup

[dabreegster]

JsRouteSnapper vs RouteSnapperMap responsibilities are unclear. Waypoint and PathEntry should maybe be the same.

... and other cleanups. The current code is a total mess, basically.

[dabreegster]

I tried to describe the current behavior as a finite state machine, in the hopes that it'd be easier to understand or visualize. Here are notes, incomplete:

• how do we characterize current state?

  • list of waypoints (snapped node or free pt)

  • freehand vs snap mode

    • holding shift, or it could be onscreen control

  • area or route mode (and then should we extend or not?)

  • mode

    • neutral
    • hovering on waypt
    • dragging (orig index, current waypt)
    • freehand at a pt
• try again with states, higher level
  • route mode, extend off
    • 0 points, hovering shows a possible point
    • 1 point, hovering shows a possible route
    • 2 points, hovering only works on existing points
  • area mode
    • < 3 points, hovering shows a possible point
    • at least 3, hovering only works on existing
• what're the events that happen?
  • mouse moves
    • what do we wind up hovering on?
    • is this a drag or not? (rewrite it)
  • click
    • might mean add a point, or might mean delete existing point
  • dblclick
  • dragstart
  • mouseup (aka dragend)
  • enter key to finish
  • keydown shift
  • keyup shift
• whats the action and possibly state transition?
• can we express pairs better?
  • click a free pt, a new waypt, an existing waypt, an intermediate pt