Move `multiline_string_handling` from unstable to preview (#4760)

* Move `multiline_string_handling` from unstable to preview

* Docs and tests

Signed-off-by: cobalt <61329810+cobaltt7@users.noreply.github.com>

* fix tests

Signed-off-by: cobalt <61329810+cobaltt7@users.noreply.github.com>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci



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Signed-off-by: cobalt <61329810+cobaltt7@users.noreply.github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>