javac-wrapper: refactoring, fixes and tests

compiler/testData/diagnostics/tests/scopes/inheritance/statics/oneInterfaceManyTimes.kt

@@ -17,14 +17,14 @@ open class K : C(), I
 
 // FILE: D.java
 
-public class D extends K, I {
+public class D extends K implements I {
     static int c = 1;
     static void baz() {}
 }
 
 // FILE: E.java
 
-public class E extends D, I {
+public class E extends D implements I {
     static int a = 1;
 }