Move task positioning tasks from WindowManagerService.mH

The CL moves task positioning tasks from WindowManagerService.mH to
TaskPositioningController.mHandler.

Bug: 64149458
Test: atest com.android.server.wm.TaskPositioningControllerTests
Change-Id: I2a8ce22a1698e008b2abd2e8f1b06886cec697b4
5 files changed