[Java][BigQueryIO] Use schema ordinals as verified hints for TableRow descriptor lookup

[khaledh]

fixes #40188

messageFromMap resolves every field with Descriptor.findFieldByName, which concatenates and hashes the fully qualified name on each call. This records each field's ordinal in SchemaInformation and uses it as a lookup hint, verified by name, with findFieldByName as the fallback.

• No cache, no shared state, no public API change.
• Required-field validation and diagnostics unchanged.
• JMH: 1.575 → 1.084 ms/op (−31%). Dataflow, production workload: −15.7% CPU/record with this change alone.

Tests: reordered descriptor (exact bytes), ordinal beyond descriptor length (fallback), required-field validation, concurrent conversion. GCP IO suite green on JDK 11 and 17.

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