### LinkConnector
Replaces the minimal-change effort of `connecting_links` with a more
reliable implementation.
- Subscribable, event-based API
- Uses browser-standard `e.preventDefault()` to cancel `before-*` events
- Uses standard `state` POJO - can be proxied without issue
- Structures code and separates concerns out of `LGraphCanvas`
- Link creation calls can now be made from anywhere, without the need
for a rewrite
- New canvas sub-components now live in `src/canvas/`
### Rendering
- Skips link segments by setting a `_dragging` bool flag on the LLink or
Reroute
- Moves some previously nested code to event listeners, configured in
the `LGraphCanvas` constructor
### Deprecation
`LGraphCanvas.connecting_links` is now deprecated and will later be
removed.
Until it is removed, to prevent breaking extensions it will continue to
be set and cleared by a legacy callback. The contents of this property
are ignored; code search revealed no exentsions actually modifying the
array.
