Fix Razor server shutdown on Windows.

On Windows, the Razor server correctly creates the pid file with
`FileAccess.Write` and `FileOptions.DeleteOnClose`.  This requires a share mode
of `FileShare.Write | FileShare.Delete` to open.  However, the
`dotnet build-server shutdown` command was opening the file with
`FileShare.Read`.  As a result, an `IOException` was being thrown and was not
handled.

This change first opens the file with the appropriate share access and also
properly handles a failure to access or read the contents of the pid file.

Additionally, an integration test was added to test that Razor server shutdown
works as expected.

Fixes #9158.

TestAssets/TestProjects/TestRazorApp/Areas/MyFeature/Pages/Page1.cshtml.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+
+namespace TestRazorApp.MyFeature.Pages
+{
+    public class Page1Model : PageModel
+    {
+        public void OnGet()
+        {
+
+        }
+    }
+}