fix(shader): fix lighting discontinuity at mirrored UV seams

[xubing0906]

Re: #

Changelog

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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.

---

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.

[xubing0906]

@cocos-robot run test cases

[github-actions]

Code Size Check Report

Wechat (WASM)	Before	After	Diff
2D Empty (legacy pipeline)	1014547 bytes	1014547 bytes	✅ 0 bytes
2D All (legacy pipeline)	2682072 bytes	2682072 bytes	✅ 0 bytes
2D All (new pipeline)	2773854 bytes	2773854 bytes	✅ 0 bytes
(2D + 3D) All	10031227 bytes	10031227 bytes	✅ 0 bytes

Web (WASM + ASMJS)	Before	After	Diff
(2D + 3D) All	16867640 bytes	16867640 bytes	✅ 0 bytes

Interface Check Report

This pull request does not change any public interfaces !

[github-actions]

@xubing0906, Please check the result of run test cases:

• Test Platform: PR-Test
• Editor Version: v4.0.0
• Task Result: PASS
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/800151bd-18cd-4e01-9094-85cd29864e24/-1
• GitHub Action: https://github.com/cocos/cocos4/actions/runs/29712562097

Task Details

[github-actions]

@xubing0906, Please check the result of run test cases:

• Test Platform: PR-Test
• Editor Version: v4.0.0
• Task Result: PASS
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/d7edbbe1-2d79-4363-9cee-97a80417bcae/-1
• GitHub Action: https://github.com/cocos/cocos4/actions/runs/29712562097

Task Details

[xubing0906]

[xubing0906]

cocos/cocos-engine#19167
cocos/cocos-engine#19169

[xubing0906]

@cocos-robot run test cases

[github-actions]

@xubing0906, Please check the result of run test cases:

• Test Platform: PR-Test
• Editor Version: v4.0.0
• Task Result: PASS
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/9a8083d7-19d8-4a57-a81e-f1f3890708f5/-1
• GitHub Action: https://github.com/cocos/cocos4/actions/runs/30086731160

Task Details

[github-actions]

@xubing0906, Please check the result of run test cases:

• Test Platform: PR-Test
• Editor Version: v4.0.0
• Task Result: PASS
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/19e7979f-d746-4301-94ca-541069089b28/-1
• GitHub Action: https://github.com/cocos/cocos4/actions/runs/30086731160

Task Details

[xubing0906]

测试例在此，case.zip，打开scene只要里面的角色额头没接缝就是对的。
正确的效果错误的效果

[jk20012001]

add:
normal = normalize(normal);
tangent = normalize(tangent);