The Javadoc for open() won't be read by anyone because it's an overridden method
of the interface and not called directly from application code.
Move doc to class documentation as this is a generic explanation about the
functionality of the class. Also added "all" to clarify that all the parameters
will be added and the order of preference just applies in case of key clashes.
PiperOrigin-RevId: 266753249
aff9e731b2