Optimization: Only expand line accessor names in extensible classes

Author: odersky

compiler/src/dotty/tools/dotc/typer/PrepareInlineable.scala

@@ -53,7 +53,8 @@ object PrepareInlineable {
      */
     abstract class MakeInlineableMap(val inlineSym: Symbol) extends TreeMap with Insert {
       def accessorNameOf(name: TermName, site: Symbol)(using Context): TermName =
-        InlineAccessorName(name).expandedName(site)
+        val accName = InlineAccessorName(name)
+        if site.isExtensibleClass then accName.expandedName(site) else accName
 
       /** A definition needs an accessor if it is private, protected, or qualified private
        *  and it is not part of the tree that gets inlined. The latter test is implemented