[Test] Add a compiler crasher test case for unsupported opened existential

types.

Author: hborla

validation-test/compiler_crashers_2/unsupported_opened_existential.swift

@@ -0,0 +1,28 @@
+// RUN: not --crash %target-swift-frontend -emit-ir %s
+
+func fetch() {
+  sryMap { return "" }
+  .napError{ $0.abc() }
+}
+
+func sryMap<String>(_ transform: () -> String) -> SryMap<String> {
+  fatalError()
+}
+
+protocol MyError {}
+extension MyError {
+  func abc() -> Void { }
+}
+
+protocol MyProto {
+  associatedtype Failure
+}
+extension MyProto {
+  func napError(_ transform: (Self.Failure) -> Void) {}
+}
+
+struct SryMap<Output> : MyProto {
+  typealias Failure = MyError & SomeClass<Output>
+}
+
+class SomeClass<T> {}