UnavailableReplicas not checked for machine deployment status update

[rishabh-11]

How to categorize this issue?

/area robustness
/kind bug
/priority 2

What happened:
The current check for whether the status update for machine deployment is needed does not consider UnavailableReplicas (See this). This can lead to an incorrect value of UnavailableReplicas in the status that will never be updated unless a scaling event happens or the machine deployment is paused or deleted.

What you expected to happen:
UnavailableReplicas in the machine deployment status should be updated correctly.

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:
Landscape issue no. 108 keeps a track of such occurrences.