feat: add bash-like linebreak (`\` at the end of line) to the REPL

[khlopkov]

Hello

Current REPL doesn't support multiline input. Found few issues marked as enhancement:

• 458

• 50

This PR suggests to interpret \ at the end of the line as a limiter for a new line like in bash.

Checklist

Dear Author :wave:, the following checks should be completed (or explicitly dismissed) before merging.

• [x] ✏️ Write a PR description, regardless of triviality, to include the value of this PR
• [x] 🔗 Reference related issues
• [x] 🏃 Test cases are included to exercise the new code
• [ ] 🧪 If new packages are being introduced to stdlib, link to Working Group discussion notes and ensure it lands under experimental/
• [ ] 📖 If language features are changing, ensure docs/Spec.md has been updated

Dear Reviewer(s) :wave:, you are responsible (among others) for ensuring the completeness and quality of the above before approval.

[helenosheaa]

Thank you for your contribution! There is a community owned fork of Flux that would be a great place to open a PR with your new feature. More context:

We are still supporting Flux, but are not doing active development on it or adding any new features to it. We still do security patches and will address any critical defects through the maintenance period. Our focus now is on features related to our latest database engine, InfluxDB 3.0, and its associated products (Cloud Serverless, Cloud Dedicated, Clustered, Edge).

[khlopkov]

Thank you! Closing the MR then and will submit a PR into the fork