[NI] Add test for KT-30300 with complex constraint system problem

compiler/testData/diagnostics/tests/inference/commonSystem/kt30300.kt

@@ -0,0 +1,21 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+// Issue: KT-30300
+
+class Inv<T>
+class InvOut<T, out K>
+
+class Sample
+
+fun <T> select(x: T, y: T): T = x
+fun <K1, V1> selectInvOut(a: InvOut<out K1, V1>, b: InvOut<out K1, V1>): InvOut<K1, V1> = TODO()
+fun <K2, V2> emptyInvOut(): InvOut<K2, V2> = TODO()
+fun <S> create(element: S): InvOut<Inv<S>, S> = TODO()
+
+fun test(s: Sample, b: InvOut<Inv<*>, Any?>) {
+    <!DEBUG_INFO_EXPRESSION_TYPE("InvOut<Inv<*>, kotlin.Any?>")!>selectInvOut(
+        b,
+        select(create(s), emptyInvOut())
+    )<!>
+}
+