Reflect Kotlin's declaration-site variance in Java signatures

compiler/testData/writeSignature/declarationSiteVariance/PropertyGetterTwoParams.kt

@@ -0,0 +1,9 @@
+class M<in K, out V>
+class X
+
+val p: M<X, X> = throw Exception()
+
+// method: namespace::getP
+// jvm signature:     ()LM;
+// generic signature: ()LM<LX;LX;>;
+// kotlin signature:  null