Issue
When creating plugins that handle node availability it is necessary to access a node's temporaryOfflineCause so that it can be examined (e.g. to find out which user set it etc.).
This can be easily done if the node is still connected (== still has a channel) but if another OfflineCause is set (e.g. because of a connection termination) it is impossible to retrieve the temporaryOfflineCause set previously using a Computer's getOfflineCause method which is the only method available to retrieve OfflineCauses.

Solution
Currently temporaryOfflineCause is a private attribute of the Node class and has been since it was added 11 years ago.

The attribute could either be made public or a getter could be added.
Since the attribute should most likely not be messed with directly from outside - since setTemporarilyOffline should be used for that - I would propose introducing a simple getter.