honor vararg calls when inferring contracts (IDEA-148862)

java/java-tests/testData/inspection/dataFlow/contractCheck/PassingVarargsToDelegate.java

@@ -0,0 +1,8 @@
+class Test {
+  private String wrap(final String wrapWith, final String token) {
+    return join(wrapWith, token, wrapWith);
+  }
+
+  @org.jetbrains.annotations.Contract("null->null; !null->!null")
+  native static <T> String join(T... elements);
+}