Move taskbar insets logic to TaskbarInsetsController

Test: TaplTestsTaskbar; manually stash/unstash taskbar, open IME
Bug: 215411414
Change-Id: I73622dc020c4f8c8b3d317fcb1dd072bcfc3d274
Merged-In: I73622dc020c4f8c8b3d317fcb1dd072bcfc3d274
6 files changed