[test] Add a fixed crasher test for SR-9199 (swiftlang#20386)

Author: jrose-apple

validation-test/compiler_crashers_2_fixed/sr9199.swift

@@ -0,0 +1,57 @@
+// RUN: %target-swift-frontend -emit-ir -o %t.ll %s
+
+// Just make sure we don't crash.
+
+protocol Publicable {
+    associatedtype PublicModel
+
+    func publicized() -> PublicModel
+}
+
+
+protocol WithReturnType {
+    associatedtype MainType
+    associatedtype ReturnType
+
+    func returnTheThing()
+}
+
+extension WithReturnType where MainType: Publicable {
+    typealias ReturnType = MainType.PublicModel
+
+    func returnTheThing() {
+        print("publicable")
+    }
+}
+
+extension WithReturnType {
+    func returnTheThing() {
+        print("not publicable")
+    }
+}
+
+extension String: Publicable {
+    struct PublicString {
+        let inner: String
+
+        init(str: String) {
+            self.inner = "Public: \(str)"
+        }
+    }
+
+    func publicized() -> PublicString {
+        return PublicString(str: self)
+    }
+}
+
+struct Controller<T> {
+
+}
+
+extension Controller: WithReturnType {
+    typealias MainType = T
+}
+
+let controller = Controller<String>()
+
+controller.returnTheThing()