Deal with corrupted files or I/O errors when reading project files

The rest of the MSBuild reading code can deal with this, but we need
to deal with it directly in this path too. Rather than force callers
to have to deal with "we can't give a host because the project file is
unreadable, so good luck", we'll just give back a host that we know
exists so the rest of the code can deal with the existing error logging
paths.

src/Workspaces/Core/MSBuild/MSBuild/BuildHostProcessManager.cs

@@ -249,10 +249,26 @@ private static BuildHostProcessKind GetKindForProject(string projectFilePath)
         // we'll load the XML of the project directly, and inspect for certain elements.
         XDocument document;
 
-        // Read the XML, prohibiting DTD processing due the the usual concerns there.
-        using (var fileStream = new FileStream(projectFilePath, FileMode.Open, FileAccess.Read))
-        using (var xmlReader = XmlReader.Create(fileStream, s_xmlSettings))
-            document = XDocument.Load(xmlReader);
+        var frameworkHostType = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? BuildHostProcessKind.NetFramework : BuildHostProcessKind.Mono;
+
+        try
+        {
+            // Read the XML, prohibiting DTD processing due the the usual security concerns there.
+            using (var fileStream = FileUtilities.OpenRead(projectFilePath))
+            using (var xmlReader = XmlReader.Create(fileStream, s_xmlSettings))
+                document = XDocument.Load(xmlReader);
+        }
+        catch (Exception e) when (e is IOException or XmlException)
+        {
+            // We were unable to read the file; rather than having callers of the build process manager have to deal with this special case
+            // we'll instead just give them a host that corresponds to what they are running as; we know that host unquestionably exists
+            // and the rest of the code can deal with this cleanly.
+#if NET
+            return BuildHostProcessKind.NetCore;
+#else
+            return frameworkHostType;
+#endif
+        }
 
         // If we don't have a root, doesn't really matter which. This project is just malformed.
         if (document.Root == null)
@@ -276,7 +292,7 @@ private static BuildHostProcessKind GetKindForProject(string projectFilePath)
             return BuildHostProcessKind.NetCore;
 
         // Nothing that indicates it's an SDK-style project, so use our .NET framework host
-        return RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? BuildHostProcessKind.NetFramework : BuildHostProcessKind.Mono;
+        return frameworkHostType;
     }
 
     public enum BuildHostProcessKind