[Feature-Request] Phase Detect Autofocus

[sebastian-student]

Start with the why:

To reliably focus a moving object in front of static background with custom autofocus region.
Currently changing the autofocus region results in contrast based autofocus typical 'focus
hunting' over hole focus range even though the IMX378 supposedly supports PDA.

Move to the what:

Focus mode utilising phase detect autofocus on supported image sensors.

Move to the how:

If you already have an idea of how this new feature could be implemented, describe it here.