feat(cdk/drag-drop): X and Y as percentage values instead of px

### Feature Description

We are developing a mobile app in which users should be able to move elements back and forth in a certain area. The position of the elements should obviously be identical for every user. However, this does not work since each user has a different smartphone and therefore a different screen width, as cdk/drag-drop works with px values. One should be able to switch from px to % in order to ensure the correct position regardless of the screen resolution (or the width of the boundary element).

首先定位存储并应用 X 和 Y 位置的 cdk/drag-drop 实现，然后检查其现有的基于像素的行为和测试。定义应如何接受百分比值，以及如何根据边界元素进行转换；当位置在不同边界宽度下保持一致，并且该行为有测试覆盖时，即视为完成。

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