Moves shelf offset into SysUI package

With this change, the shelf offset will be set directly by Launcher to
SysUI without WM being involved.

PinnedStackControllerTest is removed in this change since the only test
function is against WM.setShelfHeight. However, new tests regard
PinnedStackController should be added per b/141200935.

See also: go/pip-sysui-migration

Bug: 139016518
Test: atest PinnedStackTests
Change-Id: I606de3d8106ac12d7bf2b367877bc5bb345af3fe