Razor class libs

I noticed that if you are using razor class libs, the `controllerActionDescriptor` in `FeatureViewLocationExpander` will be null.
I added
```
if (controllerActionDescriptor == null)
{
// make sure shared stuff is searched for under the "features" folder
foreach (var location in viewLocations)
{
yield return location.Replace("Pages", "Features");
}
}
```
so that if a razor class lib would reference views/shared it still would be found. Let me know if you think this is a good idea, then I will make a pr.

Locate FeatureViewLocationExpander and investigate why controllerActionDescriptor is null when using Razor class libraries. Reproduce the views/shared lookup case described in the issue, then verify that shared views are found under the Features folder without breaking existing view-location behavior.

Written by the indexing model from the issue text.