SF: Rename functions related to mode switching

This change renames several function in SF in order to increase
readibility.

 * performSetActiveMode --> setActiveModeInHwcIfNeeded
 * setActiveModeInternal --> updateInternalStateWithChangedMode
 * setActiveMode --> setActiveModeFromBackdoor

This CL doesn't change behaviour.

Bug: 190982486
Test: m
Change-Id: I2723f66302016ffc196530f2000fce4a44524fb4