Converter tests:

Change test data files extension to "java"

j2k/tests/testData/ast/issues/kt-820.java

@@ -0,0 +1,16 @@
+//file
+package demo;
+
+class Container {
+  int myInt = 1;
+}
+
+class One {
+  static Container myContainer = new Container();
+}
+
+class Test {
+  void test() {
+    byte b = One.myContainer.myInt;
+  }
+}