[Backport 2.19-dev] issue #4514 tonumber function as part of roadmap #4287

[opensearch-trigger-bot]

Backport 342a78b from #4605.

[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch backport/backport-4605-to-2.19-dev

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[dai-chen]

New added IT failed. Need to investigate.

2025-12-11T21:45:34.8476709Z org.opensearch.sql.ppl.ConversionFunctionIT > testHex FAILED
2025-12-11T21:45:34.8488318Z     org.opensearch.client.ResponseException: method [POST], 
host [http://127.0.0.1:42695], URI [/_plugins/_ppl], status line [HTTP/1.1 400 Bad Request]
2025-12-11T21:45:34.8489206Z     {
2025-12-11T21:45:34.8489444Z       "error": {
2025-12-11T21:45:34.8489744Z         "reason": "Invalid Query",
2025-12-11T21:45:34.8490169Z         "details": "unsupported function name: tonumber",
2025-12-11T21:45:34.8490664Z         "type": "ExpressionEvaluationException"
2025-12-11T21:45:34.8491054Z       },
2025-12-11T21:45:34.8491301Z       "status": 400
2025-12-11T21:45:34.8491562Z     }

[dai-chen]

The root cause seems we didn't enable Calcite in ConversionFunctionIT and Calcite is disabled by default: https://github.com/opensearch-project/sql/blame/2.19-dev/opensearch/src/main/java/org/opensearch/sql/opensearch/setting/OpenSearchSettings.java#L173. cc: @asifabashar

[dai-chen]

Another backport PR failed due to similar reason: #4959

[dai-chen]

Created issue #4960 for broader topic regarding such boilerplate code. We will need to fix both PRs manually.

[dai-chen]

Will publish manual PR shortly.

[dai-chen]

New PR: #4963