Fix Registering ActiveProcessingPictureListener and rename callback list

The `ActiveProcessingPictureListener` was not being registered with the
broadcast list, preventing callbacks from being delivered. This change
adds the missing registration. Additionally, the variable
`mActiveProcessingPictureCallbackList` is renamed to
`mActiveProcessingPictureCallbacks` for consistency.

Bug: 412928252
Flag: EXEMPT bugfix
Change-Id: Ie13f3eadcadaad01622820a1e735825634ba719c