JS: change how signature for mangling is generated, taking into account more information. See KT-15285

compiler/frontend/src/org/jetbrains/kotlin/types/Utils.kt

@@ -36,4 +36,20 @@ internal fun hackForTypeIntersector(types: Collection<KotlinType>): KotlinType?
             ErrorTypesAreEqualToAnything.isSubtypeOf(candidate, it)
         }
     }
+}
+
+fun getEffectiveVariance(parameterVariance: Variance, projectionKind: Variance): Variance {
+    if (parameterVariance === Variance.INVARIANT) {
+        return projectionKind
+    }
+    if (projectionKind === Variance.INVARIANT) {
+        return parameterVariance
+    }
+    if (parameterVariance === projectionKind) {
+        return parameterVariance
+    }
+
+    // In<out X> = In<*>
+    // Out<in X> = Out<*>
+    return Variance.OUT_VARIANCE
 }