Implement a minimal version of MapAction

[halter73]

This issue tracks what should be included in the first PR that adds a MapAction extension method to IEndpointRouteBuilder.

Requirements:

• Support for binding [FromBody], [FromRoute], [FromQuery], [FromHeaders], [FromService] parameters.
  • [FromBody] will be JSON-only for the first iteration
  • [FromQuery] will likely not support complex types due to MVC-isms
• Serialize return value as JSON-only for first iteration
• Use [Route] attribute instead of an explicit parameter.
• HttpContext injection

Follow up:

• Benchmarks (Add benchmarks for MapAction #29915)
• Remove LINQ from startup path
• Input and output formatters
• Model binding validation
• Swagger support (IApiDescriptionGroupCollectionProvider implementation)
• MapAction filters

Is your feature request related to a problem? Please describe.

I want to be able to use MVC features like parameter binding without having to write a Controller.

Describe the solution you'd like

A MapAction extension method for IEndpointRouteBuilder that accepts controller action-like delegates.

[Tratcher]

What about [FromForm]?

[halter73]

I think [FromForm] will come later if at all because of its MVC-isms and because it's not really used much for APIs. For the first round, we're only going to support JSON for complex types. Maybe we can support it for simple stuff though.

[davidfowl]

I think you should add support [FromForm] as well, just not for complex objects (yet).