Fix problems regarding Scala 3 and sourcePositionMapper

[mkurz]

See

• feat(scala3): WIP working on scala 3 cross compilation. #390. #461 (comment)
• sourcePositionMapper of sbt doesn't work with DelegatingReporter of Dotty scala/scala3#14691
• The compiler interface should expose sourcePositionMappers so that Scala 3 can render messages with the proper positions sbt/zinc#1074 (comment)

Following commit could then be reverted eventually: e892f83

[tototoshi]

The pull request I sent to sbt/zinc has been merged.
Hopefully, the next release will fix the problem.

[mkurz]

@tototoshi Nice 👍 BTW, did you see sbt/sbt#6868, I didn't look into all of that, however has this something to do with our problem?

[tototoshi]

Yes, I am interested in this proposal.
I don't think that this proposal can be a solution to our problem with sourcePositionMappers.
However, it will be a help to make Twirl error messages more friendly in the future.