New J2K: add plain text copy-paste conversion test for new J2K

nj2k/testData/copyPastePlainText/OverrideInterface.dependency.java

@@ -0,0 +1,7 @@
+package test;
+
+import org.jetbrains.annotations.Nullable;
+
+public interface JavaInterface {
+    void subject(@Nullable String s)
+}