Convert ValuesController return types to ActionResult<T> (#351)

Addresses #339

src/Microsoft.DotNet.Web.ProjectTemplates/content/WebApi-CSharp/Controllers/ValuesController.cs

@@ -18,14 +18,14 @@ namespace Company.WebApplication1.Controllers
     {
         // GET api/values
         [HttpGet]
-        public IEnumerable<string> Get()
+        public ActionResult<IEnumerable<string>> Get()
         {
             return new string[] { "value1", "value2" };
         }
 
         // GET api/values/5
         [HttpGet("{id}")]
-        public string Get(int id)
+        public ActionResult<string> Get(int id)
         {
             return "value";
         }

src/Microsoft.DotNet.Web.ProjectTemplates/content/WebApi-FSharp/Controllers/ValuesController.fs

@@ -13,11 +13,13 @@ type ValuesController () =
 
     [<HttpGet>]
     member this.Get() =
-        [|"value1"; "value2"|]
+        let values = [|"value1"; "value2"|]
+        ActionResult<string[]>(values)
 
     [<HttpGet("{id}")>]
     member this.Get(id:int) =
-        "value"
+        let value = "value"
+        ActionResult<string>(value)
 
     [<HttpPost>]
     member this.Post([<FromBody>] value:string) =