Improve debugging support by implementing JSR-45 #9715
Description
We should port scala/scala#9121, note that unlike scala 2 we don't have a backend inliner (yet) but we do have inline def so we need to deal with positions coming from other files, this is currently handled by https://github.com/lampepfl/dotty/blob/cdfc76e2e5093dd8f70e1d582e38d2537494c0bb/compiler/src/dotty/tools/dotc/typer/Inliner.scala#L239-L240