[PR] DateTime::createFromImmutable() method

Good morning internals! I would like to propose a small addition be made to the DateTime class. https://github.com/php/php-src/pull/1145 This is my first contribution to PHP's core, beyond documentation edits. I'm not sure on the formalities that need to be taken for something like this to be considered as an addition, or if an email like this is even appropriate, so I'd absolutely welcome any guidance here. I just saw a possible opportunity for an addition and thought it would be fun to try and contribute to PHP. :) I'm not a C programmer by any means, so please forgive me if I've made any "noob" mistakes here, haha. Thank you all for your time and consideration! - Trevor