Fixed synthetic properties for method inherited from two bases

compiler/testData/codegen/boxAgainstJava/syntheticExtensions/fromTwoBases.java

@@ -0,0 +1,14 @@
+interface A {
+    String getOk();
+}
+
+interface B {
+    String getOk();
+}
+
+interface C extends A, B {
+}
+
+class JavaClass implements C {
+    public String getOk() { return "OK"; }
+}