[TypeChecker] NFC: Add a test-case for rdar://70880670

Author: xedin

validation-test/Sema/SwiftUI/rdar70880670.swift

@@ -0,0 +1,15 @@
+// RUN: %target-typecheck-verify-swift -target x86_64-apple-macosx10.15 -swift-version 5
+// REQUIRES: objc_interop
+// REQUIRES: OS=macosx
+
+import SwiftUI
+
+var foo = doesntExist // expected-error {{cannot find 'doesntExist' in scope}}
+
+struct ContentView: View {
+  var body: some View {
+    VStack {
+      Text(verbatim: foo)
+    }
+  }
+}