[IDE] NFC: Add a test-case for a fixed SourceKit crasher

Resolves: rdar://problem/41331096

Author: xedin

validation-test/IDE/crashers_2_fixed/0023-rdar41331096.swift

@@ -0,0 +1,15 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=A -source-filename=%s
+
+enum E1 {
+  case X
+  case Y
+}
+enum E2 {
+  case A
+  case B
+  case C
+}
+
+func foo() -> ([E1], [E2]) {
+  return ([.X], [.A, .B, .#^A^#])
+}