Add String to switchable classes

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -795,7 +795,8 @@ object PatternMatcher {
         (tpe isRef defn.IntClass) ||
         (tpe isRef defn.ByteClass) ||
         (tpe isRef defn.ShortClass) ||
-        (tpe isRef defn.CharClass)
+        (tpe isRef defn.CharClass) ||
+        (tpe isRef defn.StringClass)
 
       val scrutinee = plan.scrutinee