[Mvc] Improved route value transformer

[rynowak]

See: #21471

This change just include the product-side changes and just for
controllers. This addresses most the major gaps our partners have found
with dynamic route value transformers. Doesn't include anything
order-related.

If we're happy with this then I can add some tests as well as make the same change for pages.

[rynowak]

@JamesNK @pranavkm @javiercn - what do you think of this? read: #21471 first.

[rynowak]

One other alternative I thought of - we could get rid of State as a property and make this use DI or Type activation - and then we use type activation if you pass a state value.

The problem is we require the use of DI here in 3.1 - supporting both adds more choices and more to explain.

[pranavkm]

This looks great. @JamesNK could you have a look when you get a chance?

[javiercn]

🆙📅

Added a check for the state not being null and matching unit tests.

[javiercn]

@mkArtakMSFT Can you squash and merge this PR with the following title and comment?

[Mvc][Fixes #21471] Improvements to DynamicRouteValueTransformer

* Provides the ability to pass context to a given DynamicRouteValueTransformer on a per route basis.
* Requires DynamicRouteValueTransformer instances with associated state to be registered as transient.
* Enables filtering based on the results of selected endpoints by MVC.