Revert "unicode.breaks: use find-index-from instead of slices."
Revert "unicode.breaks: use find-index-from instead of slices."

This reverts commit 0aeb2174fb9cd0e91b774cf212507d3274693f99.

mcandre/factor,mcandre/factor,mcandre/factor,mcandre/factor,mcandre/factor,mcandre/factor,mcandre/factor