Sample: Issues with Antiforgery + Form + File Uploads

[rynowak]

So, given the work to add size limits to form (aspnet/HttpAbstractions#618) we're going to want the ability to configure and bypass these limits per-action/controller.

There's a few scenarios we have in mind here:

1. I have a restrictive limit set app wide to limit things by default to really small inputs. But, I want to increase the limit for a specific action. (maybe for a big form post or for file uploads)
2. I have an action that's going to accept a really large file upload - usually as an ajax action. I want to completely bypass the default buffering behavior of FormFeature and stream this directly to my storage.

We need a few specific things from MVC to support everything here we want to do:
[ ] - Make value providers lazy - #4531 - (prevent MVC from reading the form if you have no model binding)
[ ] - Create a filter/sample that removes the form value provider - #4534 - (prevent MVC from reading the form at all)
[ ] - Create a filter/sample that sets the limits on FormFeature - #4535 - (prevent antiforgery from reading the form while a 'low' limit is still in effect)

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E2E Sample
Furthermore we want an end-to-end sample of using MVC to stream a large file upload. This will include a combination of the above, and using MultipartReader + Antiforgery Header Token which are already supported.

[rynowak]

/cc @Tratcher

[kichalla]

86147eda46a476b8acc409df0eaa9b0eca730e94