Backported changes

• Actively remove Scala 2 pickles and emit synthetic TASTy attribute for copied stdlib .class files #24846
• Deprecate MapOps.KeySet, replace with private (and more performant) strict/lazy KeySet implementations #24767

Contributors

Thank you to all the contributors who made this release possible 🎉

According to git shortlog -sn --no-merges 3.8.0-RC5..3.8.0-RC6 these are:

    17  Wojciech Mazur
     5  Natsu Kagami
     1  Hamza Remmal