[C++] Replace RapidJSON with simdjson in JSON chunker #50944

Describe the enhancement requested

The JSON chunker currently uses RapidJSON to identify complete JSON values and determine JSON document boundaries when newlines_in_values is enabled.

Replace the RapidJSON-based boundary detection with simdjson while preserving the existing chunking behavior, including handling of:

• Pretty-printed JSON values containing raw newlines.
• Multiple JSON values in a single block.
• JSON values straddling block boundaries.
• Incomplete trailing JSON values.
• Invalid JSON input and existing error propagation behavior.

The new implementation should detect structural JSON boundaries and validate complete JSON candidates with simdjson.

Additional context

Parent Issue: GH-35460.

Component(s)

C++