Tag Helpers: enum attribute of nested enum type

[johnpedersen-freightways]

#196 allows writing only the enum member as the attribute value.
When using a tag helper property with a nested enum type the generated code is invalid.

class Parent {
  public enum Foo {
    Bar,
  }
}

<mytaghelper someattr="Bar" />

The generated code is like this:

__MyTagHelper.SomeAttr = global::SomeNamespace.Parent+Child.Bar;

Microsoft.AspNetCore.Mvc.Razor v1.1.1

[Eilon]

@ajaybhargavb we think this might already be fixed. Either way, please make sure there's a test for this case.

[Eilon]

3-Done?