When adding Turn Restrictions, split the from and to ways near the intersection

This is a request from several teams working with turn restrictions (including Mapbox and others). It would be useful to split turn restriction from/to ways near the turn restriction intersection.

The benefits here include:

• limit the extent of the effects of the turn restriction
• better review of turn restrictions in tools like on OSM or OSMCha or JOSM
• avoid unnecessary modification of the turn restriction (e.g. a "new" TR may end up with version 2 just because a split happened far away after it was added).

For example:

It's pretty easy to tell what was changed here because the turn restriction is scoped tightly to the intersection:

Not so much for this one, which covers a large portion of Detroit:

(Both changes were made with iD - the first example just happened to involve ways that were already split around there).

cc @maning @planemad

The issue names no files, tests, or entry points. Review iD’s current turn-restriction editing flow against the screenshots and stated benefits, then determine the required behavior and scope. Done should mean that adding a restriction splits its from and to ways near the intersection and keeps the restriction tightly scoped.