This commit adds support for exposing endpoint operations over HTTP.
Jersey, Spring MVC, and WebFlux are all supported but the programming
model remains web framework agnostic. When using WebFlux, blocking
operations are automatically performed on a separate thread using
Reactor's scheduler support. Support for web-specific extensions is
provided via a new `@WebEndpointExtension` annotation.

Closes gh-7970
Closes gh-9946
Closes gh-9947