Allows different menu icons on each side of a notification.

This change modifies NotificationMenuRow such that it is now able to
display a different set of icons depending on whether the user swipes
left or right.

No change is made to the current set of icons - all current icons are
still displayed on both sides - but this will enable a followup CL to
replace the buttons to the right of the notification with block and
silence buttons per the designs for the new interruption model.

Bug: 116622974
Test: atest NotificationMenuRowTest
Change-Id: I459441353099d45f348b8299a1fb140790b0697e