Reflect Kotlin's declaration-site variance in Java signatures

compiler/testData/writeSignature/declarationSiteVariance/InOfOutInOutPosition.kt

@@ -0,0 +1,10 @@
+class In<in T>
+class Out<out T>
+class X
+
+fun f(): In<Out<X>> = throw Exception()
+
+// method: namespace::f
+// jvm signature:     ()LIn;
+// generic signature: ()LIn<LOut<+LX;>;>;
+// kotlin signature:  ()LIn<LOut<LX;>;>;