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

まだ誰も着手していません。

### 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

```python

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 https://github.com/matplotlib/matplotlib/issues/22223#issuecomment-1011957191 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.

まず ConnectionPatch とアノテーションの座標処理を読み、その後、issue #22223 で提案されている座標系のファクタリング方針を確認してください。ConnectionPatch が、接続のセマンティクスを維持したまま、artist coordinates を含む、ここで説明されているアノテーション座標の形式をサポートすれば、作業は完了です。

索引モデルが issue の本文から書いたものです。