Fixes: #4597 Parse URI path with an endpoint

[rynowak]

Adds functionality to LinkParser to parse a URI path given a way to
find an endpoint. This is the replacement for various machinications
using the global route collection and RouteData.Routers in earlier
versions.

For now I'm just adding a way to do this using Endpoint Name since it's
a pretty low level feature. Endpoint Name is also very direct, so it
feels good for something like this.

Example usage:

[HttpPut]
[Route("/Products/{id}", Name = "ProductsRoute")]
public async Task<IActionResult> AddRelatedProduct(int projectId, string path)
{
   var values = parser.ParsePathByEndpointName("ProductsRoute", path);
   var relatedId = (string)values["id"];

   // Do something with this information
}

[rynowak]

@JamesNK looking for your COOL high level feedback on this before adding tests.

[rynowak]

This is also pretty simple and straightforward compared to what we have today 👍

[rynowak]

There's a few more decisions here to be made like - does this apply default values? Does this run constraints? I'm planning to reach out to some of the folks that asked for this feature and poll them.

[rynowak]

@oferns @mgolois - I'm looking at adding an API to address your feedback here: #4597

Could you take a look at this and let me know what you think?

[JamesNK]

Seems alright.

It does feel a little odd to have matching on link generator. Consider whether a new type makes sense. LinkParser?

[oferns]

How/where is GetEndpoints implemented? This was my issue, getting access to the routes/endpoints that used to be in RouteData.Routes

[rynowak]

Get endpoints is implemented on the base class.

If you want a list of all of the endpoints in the app, you do do that by grabbing EndpointDataSource from DI. If you want the endpoint that matched the current request, use this. https://github.com/aspnet/AspNetCore/blob/425c196cba530b161b120a57af8f1dd513b96f67/src/Http/Http.Abstractions/src/Routing/EndpointHttpContextExtensions.cs

[rynowak]

@JamesNK - ready for review. I decided to go with a separate class.

[rynowak]

@JamesNK updated

[rynowak]

@JamesNK updated