Reflect Kotlin's declaration-site variance in Java signatures

compiler/testData/writeSignature/declarationSiteVariance/PropertySetterIn.kt

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