Build response with just ServerRequestInterface object (improved PSR-7 compatibility)

[g105b]

Currently, the Request is build in the Lifecycle, because it is expected that go.php is the entry point from a traditional web server, running PHP-FPM.

However, there is lots of room for improvement with the way PSR-7 is handled.

There should be an alternative function to start to call that is passed the PSR-7 Request object already constructed. This is how servers like React's HTTP work.

There will be no obvious benefit to the developer or the user for doing all this work (apart from the project will be more in line with PSR-7's intentions), but it will enable things like #304 to be implemented using React.

[g105b]

May be useful for PHP.Gt/Lambda - however this could be a bit simpler than it sounds: change start to take an optional PSR-7 request object, and if supplied, call handlePsr7Request, otherwise handleFpm.

[g105b]

Closed by RequestFactory::createServerRequestFromGlobalState()