Do not finish activity if with taskOverlay

Respect the taskOverlay policy to prevent finishing activity if
launch with clear-task or clear-top flags. Meanwhile rename the
performclearTask related function.

Bug: 216392957
Test: atest CtsWindowManagerDeviceTestCases:StartActivityTests
      atest WmTests:TaskTests
      atest WmTests:RootTaskTests
      atest WmTests:LockTaskControllerTest
Change-Id: I5542fd7905c816aedfff633f0331ccd00b639324