Some highlights
- `getSiblingAndChildVertices` are expensive, so they're saved and called less frequently
- draw touch targets for all the visible vertices
- remove redundant css classes and `setClass` function
(re: #3003 / #4602)
For now, drawHover is commented out. Still not sure what I will do with it.
This means that things flicker a bit when dragging, also connecting nodes
(and closing lines) does not currently work.
There was lot going on preventing the vertices from rendering while dragging.
1. `modeDragNode` needed a proper `selectedIDs()` function that works like other
modes.. Many other places in iD (including the vertex renderer) call `context.selectedIDs()`..
This means that `modeDragNode` needs a new function `restoreSelectedIDs()` to do what
`selectedIDs()` was previously doing (a place to store selectedIDs so that we
can reselect those entities after the user is done dragging a node in select mode)
2. Just so many things in svg/vertices.js
- siblingAndChildVertices was missing some things for points that we render
as vertices (points in wireframe, points with directions)
- the sibling vertices weren't being included in the `filter` function, so
would disappear when doing differenced/extent redraws
- probably some other things
(closes#3824)
When hovering, there is also a companion `vertex-hover` element that might
sometimes get selected, and doesn't have the sibling class that enables drag.
This is because #surface can be transformed during a partial redraw
and d3.mouse() returns transformed point, not the real screen point.
a2cf4f32ec/src/point.js (L4-L9)
