Add top-level enum test

Ironically we can't test it on C# because the driver assumes
the partial class exists.

test/inputs/schema/top-level-enum.1.json

@@ -0,0 +1 @@
+"one"

test/inputs/schema/top-level-enum.schema

@@ -0,0 +1,8 @@
+{
+    "type": "string",
+    "enum": [
+        "one",
+        "three",
+        "two"
+    ]
+}

test/languages.ts

@@ -49,7 +49,9 @@ export const CSharpLanguage: Language = {
     "31189.json" // JSON.NET doesn't accept year 0000 as 1BC, though it should
   ],
   skipMiscJSON: false,
-  skipSchema: [],
+  skipSchema: [
+    "top-level-enum.schema" // The code we generate for top-level enums is incompatible with the driver
+  ],
   rendererOptions: {},
   quickTestRendererOptions: [{ "array-type": "list" }, { "csharp-version": "5" }, { density: "dense" }],
   sourceFiles: ["src/Language/CSharp.ts"]