Streamline xanchor and yanchor names for center/middle

The 'xanchor' property is an enumeration that may be specified as:
- One of the following enumeration values:
['auto', 'left', 'center', 'right']

The 'yanchor' property is an enumeration that may be specified as:
- One of the following enumeration values:
['auto', 'top', 'middle', 'bottom']

This is for plotly 6.3.0 trying to use fig.add_annotations() but it likely applies everywhere where xanchor and yanchor are used.

It does make sense that for the extremes of the bounding box left right top bottom, the names are different, but why is 'center' used for x direction and 'middle' for y direction? This distinction seems artifical to me and I wonder why this was chosen?

I propose to streamline the naming conventions, but now for backwards compatibility to at least accept both center/middle for x/yanchor.

エントリポイント fig.add_annotations() から始めて、xanchor と yanchor の値がどのように検証されているかを確認してください。同じ検証が他の場所でも共有されているかを確認し、その後、関連するテストを確認してください。完了条件には、適切な場合に center と middle の両方を後方互換で受け入れ、既存の値が引き続き機能することを含めてください。