Return the default touch mode for dead displays

Certain race conditions may lead to client code trying to manipulate
(like adding an window) an already gone virtual display. This CL changes
WMS#isInTouchMode to return the default touch mode in case the display
passed as argument is already gone.

Fix: 280671905
Test: atest FrameworksCoreTests
Test: atest WmTests:WindowManagerServiceTests
Test: atest CtsInputTestCases:android.input.cts.TouchModeTest
Change-Id: Iea61f82ec1945ba0b65ce8af4896b5fb9923af6e