Add header protection for Taskbar All Apps search bar.

Works similar to ActivityAllAppsContainerView<->ScrimView
implementation, except utilizes AbstractSlideInView's builtin scrim.

Test: Manual
Flag: ENABLE_ALL_APPS_SEARCH_IN_TASKBAR=false
Bug: 216683257
Change-Id: Ide41ac47ecffc232fffac34c6bfdda67c1da549d