Added firstLine function to extract the first line from the multi-line string

[mkmkme]

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• New Feature

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Added firstLine function to extract the first line from the multi-line string. This closes #51172.

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

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[mkmkme]

Added firstLine to aspell-dict.txt and rebased on the top of current master

[kardymonds]

For one line you can just select firstLine(materialize('foo\nbar\nbaz'))

[mkmkme]

Thanks, that's good to know!
I'll probably prefer leaving a table with multiple values because it creates a tiny chance it will trigger the vector handler for the function. Do you know btw if it can be triggered deterministically?

[kardymonds]

If this case (from current test) with three lines (ColumnString) is meant, then I don’t know. Or what vector do you mean?
(additionally FunctionStringToString has useDefaultImplementationForConstants = true, which means that the Const and non Const expression will be processed the same way.)

[mkmkme]

Rebased and resolved conflicts in documentation

[vdimir]

👍