Converter tests:

Change test data files extension to "java"

j2k/tests/testData/ast/issues/kt-1016.java

@@ -0,0 +1,9 @@
+//file
+package demo;
+
+class C {
+  private final int i;
+  public C(int i) {
+    this.i = i;
+  }
+}