[ES|QL] fix multiline comment syntax highlighting

[drewdaemon]

Summary

Highlighting bug fix

Close #197250

Other stuff

This PR also moves tokenizer logic to kbn-esql-ast package, abstracting it from Monaco. Monaco will still drive the tokenizer requirements, but there are a couple of benefits to this change.

1. Cleaner code. Separating it from Monaco constructs simplifies the core logic and increases understandability.
2. It may make sense to divorce the tokenizer from Kibana eventually along with the other highly-ANTLR-coupled stuff. I could see it powering syntax highlighting in EUI for example (Add ES|QL syntax highlighting to `EuiCodeBlock` and `EuiMarkdown` components eui#8046), and certainly in IDEs.

Checklist

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

[elasticmachine]

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