Add test for builtIn stub builder and decompiler

These test are by no means exhaustive, the correctness of the subsystem relies on it sharing code with well-tested js-decompilation

idea/testData/decompiler/builtIns/Any.text

@@ -0,0 +1,12 @@
+// IntelliJ API Decompiler stub source generated from a class file
+// Implementation of methods is not available
+
+package kotlin
+
+public open class Any public constructor() {
+    public open operator fun equals(other: kotlin.Any?): kotlin.Boolean { /* compiled code */ }
+
+    public open fun hashCode(): kotlin.Int { /* compiled code */ }
+
+    public open fun toString(): kotlin.String { /* compiled code */ }
+}