deprecate Collections.unfoldLeft

[xuwei-k]

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Helpful things

Fixes

Purpose

deprecate unfoldLeft. use scala.Seq.unfold

Background Context

• Scala std lib add Seq.unfold since 2.13. https://github.com/scala/scala/blob/7952071b88a85e2502e9ecd4e8bd57040d9448f5/src/library/scala/collection/Factory.scala#L114-L124
• playframework dropped Scala 2.12 Drop Scala 2.12 and sbt 1.3 (and 0.13.x leftovers) #10956

References