Add body parsing functionality in Request object

[l0gicgate]

Currently we do not parse any incoming data in the Request object. All that functionality has been moved to the Slim-Http decorators repository.

We should by default at least support the incoming form data in the $_POST object and JSON.

[dominikzogg]

$body = (new StreamFactory())->createStreamFromFile('php://input');

[l0gicgate]

$body = (new StreamFactory())->createStreamFromFile('php://input');

We need to do this in addition to parsing the bodies different content types.

[dominikzogg]

@l0gicgate i try to create a PR, but its hard to test (php://input) is not writeable

[dominikzogg]

@l0gicgate adding php://input and use it for parsed body are two topics, please fix one after the other, cause parsed body from php://input it not a hard requirement for psr-message

[l0gicgate]

@dominikzogg I'm fine with adding a stream wrapper dev dependency like https://packagist.org/packages/mikey179/vfsStream for unit testing so we can wrap it and test it.

[dominikzogg]

@l0gicgate i didn't find any working example mocking php://input with vfsStream

[dominikzogg]

#110

[dominikzogg]

https://github.com/slimphp/Slim-Psr7/pull/110/files#diff-ea033125b85265ce3adf4e102a8d58bbR117

[odan]

Slim 4 has this feature already included in the BodyParsingMiddleware: https://github.com/slimphp/Slim/blob/4.x/Slim/Middleware/BodyParsingMiddleware.php

Do we really want to maintain the same feature 3 times? (1. slim/slim, 2. slim/http and now also in 3. slim/psr7)