Default true -Yrepl-{class-based,use-magic-imports}

[dwijnand]

This makes the following changes to the REPL the default behaviour:

• it now uses the "class-based wrappers" implementation, see [2.12] Improve -Yrepl-class-based #8712
  • among other benefits, this reduces the tendency for e.g. parallel collections to deadlock in the REPL
• it now uses the "magic imports" implementation to reduce wrapping, see SI-6623 -Yrepl-use-magic-imports avoids nesting $iw wrappers #8576
  • this improves performance in long sessions

Fixes scala/bug#9076

[som-snytt]

BTW, there's the old help text that explains boolean flags default to off. You could add, "except when they don't."

[lrytz]

✨

[SethTisue]

@dwijnand can I ask you to improve the PR description to make it clear to 2.13.2 users what the user-visible implications of this are?

[dwijnand]

Done. (Gave short introductions but didn't duplicate the entire descriptions - feel free to adapt and/or ping me again about specifics.)

[SethTisue]

@dwijnand I added a couple highlights