[ES|QL] use lexer from elasticsearch

[drewdaemon]

Summary

Part of #173817

Up till now, we had to define our own lexer rules for our client-side ES|QL validation. This was because we were using an unofficial ANTLR package (before the official ANTLR had typescript support).

Now that we are using the official ANTLR library (as of #177211), we no longer have to encode case insensitivity into the lexer rules themselves because the caseInsensitive option is now available to us.

This means we can adopt the very same definitions that Elasticsearch uses as long as we set caseInsensitive (Elasticsearch handles case insensitivity at runtime).

Checklist

• Unit or functional tests were updated or added to match the most common scenarios

[drewdaemon]

/ci

[kibana-ci]

💚 Build Succeeded

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• Commit: 7cd8fb3

Metrics [docs]

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@elasticmachine merge upstream

[stratoula]

Fantastic!! 🚀

[stratoula]

I am super happy for this change! LGTM! Thanx Drew