PHPLIB-1600 Accept stdClass objects in BSONDocument constructor

[GromNaN]

Fixes PHPLIB-1600
Fixes #1549

Only stdClass objects are allowed, because other types of objects can have private/protected properties and we don't what to define the rule for this properties (keep or skip).

[jmikola]

This is essentially a test of ArrayObject itself. I think it'd be preferable to test bsonSerialize() (note: jsonSerialize() has the same implementation), so we can see what would actually get serialized to BSON.

My concern is that we should preserve the same encoding behavior as the extension, which will only encodes public properties.

See: https://3v4l.org/47VCv#v8.4.1

I think it's bit strange that the encoded names for protected and private properties still end up in output from ArrayObject::getArrayCopy(), and are preserved when casting back to an object. It's certainly odd that the stdClass instance resulting from that cast ends up with non-public properties, but that's likely an oddity of PHP itself.

If we can get away with only accepting stdClass|array, that might circumvent this issue.

[GromNaN]

Thanks, I followed your suggestion on allowing only array|stdClass. That covers the request.

[jmikola]

LGTM although I think you can remove two lines from the test case.