cycle: clarify the lifecycle of window switcher

cycle: clarify the lifecycle of window switcher

This commit clarifies the lifecycle of the window switcher (cycle) by:
- init_cycle(): initializes the window switcher (e.g. OSD).
- update_cycle(): updates the window switcher states including OSD,
  preview and outlines.
- destroy_cycle(): clears all the window switcher states.

This commit temporarily regresses by not trying to preserve the selected
view when a view is destroyed. This will be addressed in the next commit.