[Fixes #1283] Add functional tests for WebAPI-style controllers returning HttpContent
DateTimeOffset doesn't have a TypeConverter in Mono
Adding support for inheriting tag helpers from _ViewStart files

Fixes #1166
Fixing doc comments
[Fixefor #860]- Adding Support for [FromFormData] [FromQuery] and [FromRoute],
also updates FromBody to use the new pattern for model binding.
IServiceProvider.GetService now returns null for missing services

Previously GetService would throw if the requested service was missing.
This commit updates MVC to account for the change in behavior.
Replace calls to GetService<T> with GetRequiredService<T>

Even though GetService<T> still exists, GetRequiredService<T> preserves
the old behavior of throwing for missing services.