Rename the methods to easier understand what they do

Because it is not clear to understand what these two methods do,
we rename them.
(1)updateVisibleActivitiesLocked()
(2)updateVisibleActivitiesChangedLocked

Bug: 235296082
Test: atest VoiceInteractionSessionVisibleActivityTest
Change-Id: Id7db3a0dc9c2a17276ae213223fa3dd6ae572b9f