[72/n] Avoid creation for input surface when not used

In some cases reachability is not enabled even if the letterbox surfaces
are visible. This happens, for instance, when the letterbox happens in
Desktop Windowing.

Flag: EXEMPT Refactoring
Bug: 426435032
Test: atest WMShellUnitTests:LetterboxControllerStrategyTest
Test: atest WMShellUnitTests:MixedLetterboxControllerTest
Test: atest WMShellUnitTests:ActivityLetterboxLifecycleEventFactoryTest
Test: atest WMShellUnitTests:TaskInfoLetterboxLifecycleEventFactoryTest

Change-Id: I3d6508f559486f2d3aa430c9ad129373cd5d0318