Use StringBuilder instead of StringBuffer (thanks @smarter)

StringBuffer is synchronized thus is slower.

Author: liufengyun

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

@@ -298,7 +298,7 @@ object NameOps {
      *  `<return type><first type><second type><...>`
      */
     def specializedFunction(ret: Type, args: List[Type])(using Context): Name =
-      val sb = new StringBuffer
+      val sb = new StringBuilder
       sb.append(name.toString)
       sb.append(nme.specializedTypeNames.prefix.toString)
       sb.append(nme.specializedTypeNames.separator)