MDEV-40174: Remove unnecessary double parsing JSON document

[VasuBhakt]

Fixes MDEV-40174

Problem

The json_normalize_engine function, used by json_normalize, calls json_valid_engine before processing. The processing reparses the same JSON document that json_valid already processed.

Solution

Removed the redundant json_valid_engine pre-check to eliminate double-parsing, and integrated error handling directly into the normalization engine:

1. Catch Empty Strings: Removed DBUG_ASSERT(0) for uninitialized values and instead return an error directly in json_normalize_engine if root.type == JSON_VALUE_UNINITIALIZED.

2. Catch Trailing Garbage on Scalars: Updated json_norm_build to enforce a full scan to the end of the document for scalar values (like numbers/strings) using while (json_scan_next(je) == 0). This ensures that trailing garbage correctly triggers a syntax error, matching the strict validation previously handled by json_valid_engine.

3. Propagate Syntax Errors: Updated json_normalize_engine to explicitly check and fail if je->s.error is set during the build phase.

Version

The change is directed at versions 10.11, 11.4, 11.8, and should also fix 12.3. The PR is based on branch 10.11, being the lowest affected branch.

[gemini-code-assist]

Caution

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[CLAassistant]

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