Add a specialized withEncoding() for NativeRope

Author: eregon

src/main/java/org/truffleruby/core/rope/NativeRope.java

@@ -190,6 +190,10 @@ public String toString() {
 
     @Override
     public Rope withEncoding(Encoding newEncoding, CodeRange newCodeRange) {
+        return withEncoding(newEncoding);
+    }
+
+    public NativeRope withEncoding(Encoding newEncoding) {
         return new NativeRope(pointer, byteLength(), newEncoding, UNKNOWN_CHARACTER_LENGTH, CodeRange.CR_UNKNOWN);
     }
 

src/main/java/org/truffleruby/core/rope/RopeNodes.java

@@ -1054,7 +1054,7 @@ protected Rope withEncodingSameEncoding(Rope rope, Encoding encoding) {
 
         @Specialization(guards = "rope.getEncoding() != encoding")
         protected Rope nativeRopeWithEncoding(NativeRope rope, Encoding encoding) {
-            return rope.withEncoding(encoding, CodeRange.CR_UNKNOWN);
+            return rope.withEncoding(encoding);
         }
 
         @Specialization(