Release Notes:

- N/A

Ref https://github.com/longbridge/gpui-component/pull/1956 extract my
fork version of `anchored.rs` to let GPUI to support position Anchored
at center.


https://github.com/user-attachments/assets/8d0230ed-4b75-440b-b8c3-9bde3decd141

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>