Transform CharSequence.length to property

compiler/testData/codegen/boxWithJava/collections/charSequence/charSequence.kt

@@ -1,7 +1,5 @@
 open class A : CharSequence {
-    override fun length(): Int {
-        throw UnsupportedOperationException()
-    }
+    override val length: Int = 123
 
     override fun get(index: Int) = 'z';
 
@@ -24,5 +22,13 @@ fun box(): String {
     if (b.get(1) != 'a') return "fail 12"
     if (a.get(1) != 'z') return "fail 13"
 
+    var cs: CharSequence = a
+    if (a.length != 123) return "fail 14"
+    if (cs.length != 123) return "fail 15"
+
+    cs = b
+    if (b.length != 456) return "fail 16"
+    if (b.length != 456) return "fail 17"
+
     return J.foo();
 }