fix(ui): 修复slider组件在不同锚点下进度计算错误

[orchid-world]

Re: #4163 【修复】Slider 组件在不同锚点配置下进度值计算错误问题

Changelog

• 修复 Slider 组件在自定义锚点（非默认 (0.5, 0.5)）下进度值计算偏差的问题
• 参考2.x pr：setting the anchor point causes the slider to display an error cocos-engine#4163

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Continuous Integration

This pull request:

• needs automatic test cases check.

  Manual trigger with @cocos-robot run test cases afterward.

• does not change any runtime related code or build configuration

  If any reviewer thinks the CI checks are needed, please uncheck this option, then close and reopen the issue.

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Compatibility Check

This pull request:

• changes public API, and have ensured backward compatibility with deprecated features.
• affects platform compatibility, e.g. system version, browser version, platform sdk version, platform toolchain, language version, hardware compatibility etc.
• affects file structure of the build package or build configuration which requires user project upgrade.
• introduces breaking changes, please list all changes, affected features and the scope of violation.

[github-actions]

Code Size Check Report

Wechat (WASM)	Before	After	Diff
2D Empty (legacy pipeline)	1010312 bytes	1010312 bytes	✅ 0 bytes
2D All (legacy pipeline)	2675935 bytes	2675976 bytes	⚠️ +41 bytes
2D All (new pipeline)	2767673 bytes	2767714 bytes	⚠️ +41 bytes
(2D + 3D) All	10024669 bytes	10024710 bytes	⚠️ +41 bytes

Web (WASM + ASMJS)	Before	After	Diff
(2D + 3D) All	16843237 bytes	16843278 bytes	⚠️ +41 bytes

Interface Check Report

This pull request does not change any public interfaces !

[github-actions]

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