[ENH]: expand connectionPatch coords to support all annotation coords #26440

Problem

ConnectionPatch is described as annotation w/o text in the tutorial and as a function for connecting two aribtrary points in its docs and it would be very helpful if those two points could be artists. Since annotation supports this, I'm doing a lot of

arrow = ax.annotate("", (x1, y1), (x2, y2), xycoords=A1, textcoords=A2, arrowprops=dict(arrowstyle='-|>'))
label = ax.annotate("label", (xp, yp), xycoords=arrow)

and I'd really rather prefer to use the object with "connect thing" semantics for connecting things and the object with "label things" semantics for labeling.

Proposed solution

@anntzer proposed factoring out the annotation coordinate system in #22223 (comment) and that's the approach I'd advocate here -> pull out the coordinate logic into its own logic and then have ConnectionPatch call out to that function.