Support foreign thenables in resolve()

[jsor]

Allow foreign promises to be turned into trusted promises by checking method_exists($promiseOrValue, 'then').
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/resolve

[clue]

👍 Trivial implementation and huge step for interoperability with non-react libs

[jsor]

Released in v2.4.0.