scala version specific source directories

[gregor-i]

@theon I've implemented scala version specific source directories as suggested in your comment.

Regarding scala.js: as far as I know, scala.js won't support scala 3 any time soon. Source

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##             scala3-type-class-derivation     #347   +/-   ##
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  Coverage                                ?   95.21%           
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  Files                                   ?       31           
  Lines                                   ?     1171           
  Branches                                ?       37           
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  Hits                                    ?     1115           
  Misses                                  ?       56           
  Partials                                ?        0           

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[theon]

Thanks. This looks great!

Can see all the Scala 2 builds are passing and Scala3 is just failing because of the scoverage plugin, which I am happy to disable for Scala3 for the meantime.

I'll take another look at Scala.js as that post seems to suggest it is already supported for Scala3

What did it take to add Scala.js support in Scala 3? How did we manage to do the necessary work in less than 3 months, whereas Scala.js for Scala 2 took 7 years to mature?