docs: include all feature introductions in the document

[jujn]

What this PR does / why we need it?

①修复 DisableStringArrayUnwrapping 特性说明不太准确；
②在文档中补充了所有遗漏介绍的特性；
③重构了文档中介绍特性的方式（分功能、分块介绍）

Summary of your change

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

[wenshao]

Review: PR #4035 — docs: include all feature introductions in the document

Verdict: Request Changes — 1 Critical issue found, 3 Suggestions.

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[Critical] SupportAutoType missing deprecation and security warning

Files: docs/features_cn.md (JSONReader.Feature table), docs/features_en.md (JSONReader.Feature table)

SupportAutoType is marked @Deprecated in the source code (JSONReader.java:6210), with javadoc stating "This feature is deprecated and should not be used in production code" and recommending AutoTypeBeforeHandler. The docs present it as a regular feature with no deprecation or security warning.

Since autoType is a known fastjson attack vector, this is security-relevant.

Suggested fix: Add a deprecation note in both CN and EN docs, e.g.:

• CN: "（已弃用，不推荐在生产环境使用，建议使用 AutoTypeBeforeHandler）"
• EN: " (Deprecated, not recommended for production use; use AutoTypeBeforeHandler instead)"

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[Suggestion] JSONPath.Feature.DisableStringArrayUnwrapping javadoc not updated

File: core/src/main/java/com/alibaba/fastjson2/JSONPath.java:1646-1650

This PR fixed the same incorrect javadoc in JSONReader.java, but JSONPath.java still says "When enabled, JSON arrays containing a single string element will be unwrapped to just that string value" — the opposite of actual behavior.

Suggested fix: Apply the same javadoc correction used in JSONReader.java.

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[Suggestion] MapSortField best practice recommendation is misleading

Files: docs/features_cn.md:272, docs/features_en.md:274

Best practices suggest using MapSortField to "maintain field order" / "keep field order", but the feature actually sorts keys alphabetically (not preserving insertion order) and is @Deprecated in favor of SortMapEntriesByKeys.

Suggested fix: Replace with SortMapEntriesByKeys and correct the description to "deterministic key ordering (e.g., signature verification)".

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[Suggestion] FieldBased description typo in CN doc

File: docs/features_cn.md:47 (JSONReader.Feature table)

Description says "基于字段序列化" but JSONReader handles 反序列化 (deserialization).

Suggested fix: Change "序列化" to "反序列化".

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— qwen3.6-plus via Qwen Code /review

[jujn]

done.