Add anchor property in the SliderJoin property node

[ShuffleWire]

Is your feature request related to a problem? Please describe.
When using SliderJoin properties, I can't use (= there is no) anchor property. I do understand why (a translation don't need it), but visually it would be nice to have one.
Especially when setting up the axis of the join, it could be difficult when the interesting point is far from the origin. I have to visually ensure parallelism between my axis join and the "physical" axis.
Currently, the axis is drawn passing by the origin, which is sometimes not very usable.

Describe the solution you'd like
Add an anchor in SliderJoin property, to make it consistent with others joins, and ease axis placement.

Describe alternatives you've considered
I would otherwise add a new transform node between, to bring a new origin where I'm working, but it's not very handy.

[ShuffleWire]

Additionally, we could display some sort of "dot" where the anchor is, which would be applicable to any sort of join as well.