Generate JVM-compatible names for doc artifacts

We used to put the position of the doc artifact symbols
inside their names, which created a name that is not JVM-compatible.
This commit uses the fresh name creators to generate a fresh name for
every symbol introduced by the documentation.

The name is a fresh name composed of the name of the symbol that owns
the documentation, suffixed by `$doc`.

Author: Duhemm

compiler/src/dotty/tools/dotc/core/Comments.scala

@@ -121,7 +121,7 @@ object Comments {
 
           tree match {
             case tree: untpd.DefDef =>
-              val newName = (tree.name.show + "$" + codePos + "$doc").toTermName
+              val newName = ctx.freshNames.newName(tree.name, NameKinds.DocArtifactName)
               untpd.DefDef(newName, tree.tparams, tree.vparamss, tree.tpt, tree.rhs)
             case _ =>
               ctx.error(ProperDefinitionNotFound(), codePos)

compiler/src/dotty/tools/dotc/core/NameKinds.scala

@@ -290,6 +290,7 @@ object NameKinds {
   val SkolemName              = new UniqueNameKind("?")
   val LiftedTreeName          = new UniqueNameKind("liftedTree")
   val SuperArgName            = new UniqueNameKind("$superArg$")
+  val DocArtifactName         = new UniqueNameKind("$doc")
 
   /** A kind of unique extension methods; Unlike other unique names, these can be
    *  unmangled.