JVM_IR: add test for signatures of flexible types

compiler/testData/codegen/boxInline/signatureMangling/flexibleType.kt

@@ -0,0 +1,16 @@
+// TARGET_BACKEND: JVM_IR
+// WITH_RUNTIME
+// FILE: UseFlexibleType.java
+import java.util.List;
+
+public class UseFlexibleType {
+    static public List<String> useList(List<String> arg) {
+        return arg;
+    }
+}
+
+// FILE: use.kt
+inline fun callTest() = UseFlexibleType.useList(listOf("OK"))
+
+// FILE: box.kt
+fun box() = callTest()[0]