[optimization] free string memory after JSON is parsed.

[dumganhar]

V8's garbage collector only take care of JS Heap and ignore the external string size. So ExternalStringResource::Dispose may be delayed which will cause memory in high value.

Re: #17012

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.

Greptile Summary

Optimized memory management for external strings in JSON parsing by ensuring prompt memory release.

• Modified native/cocos/bindings/jswrapper/v8/Utils.cpp to call delete this in ExternalStringResource::Dispose.
• Removed atomic counter gExternalCount for tracking external strings.
• Explicitly cleared and shrunk string memory post-parsing to reduce memory usage.
• Adjusted native/cocos/bindings/jswrapper/v8/Object.cpp to align with new memory management logic.

[github-actions]

Interface Check Report

This pull request does not change any public interfaces !

[dumganhar]

@cocos-robot run test cases

[greptile-apps]

LGTM

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[greptile-apps]

LGTM

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[greptile-apps]

LGTM

_{3 file(s) reviewed, no comment(s)
Edit PR Review Bot Settings}

[github-actions]

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

• Test Platform: PR-Test
• Editor Version: v3.8.4
• Task Result: FAIL
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/312afd74-660f-42f2-b750-9ec54122db69/-1
• GitHub Action: https://github.com/cocos/cocos-engine/actions/runs/10196048915

Task Details

Platform	build	boot	runned	crashScene	FailScene
web-mobile	PASS	PASS	PASS
ios	FAIL		FAIL
mac	FAIL		FAIL

[github-actions]

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

• Test Platform: PR-Test
• Editor Version: v3.8.4
• Task Result: FAIL
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/9f971b1d-5dee-4ea5-98e0-ca1f2d701b0f/-1
• GitHub Action: https://github.com/cocos/cocos-engine/actions/runs/10196048915

Task Details

Platform	build	boot	runned	crashScene	FailScene
windows	FAIL		FAIL
android	FAIL		FAIL
wechatgame	PASS	FAIL	FAIL