Test HTTPServer with urls that match the method
Test HTTPServer with urls that match the method

- Enhance the test HTTPServer by adding /head, /get, /post, /put and
  /delete URLs that require the HTTP method to match the endpoint and
  return the headers in the request as a JSON body.

- Add extra validation when parsing the request method token.

apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation