Report error on more than one class bound for type parameters

Such code may behave unexpectedly when compiled to JVM

compiler/testData/codegen/box/extensionProperties/genericValMultipleUpperBounds.kt

@@ -1,8 +1,10 @@
-val <T> T.valProp: T where T : Number, T : Int
+import java.io.Serializable
+
+val <T> T.valProp: T where T : Number, T : Serializable
     get() = this
 
 fun box(): String {
     0.valProp
 
     return "OK"
-}
+}