[20/n] Create event spy surface in LetterboxInputController

LetterboxInputControl to handle the lifecycle of the spy Surface
we use to detect events related to Letterbox reachability.

Flag: com.android.window.flags.app_compat_refactoring
Bug: 371500295
Test: atest WMShellUnitTests:LetterboxInputControllerTest
Test: atest WMShellUnitTests:InputChannelSupplierTest
Test: atest WMShellUnitTests:SurfaceBuilderSupplierTest
Test: atest WMShellUnitTests:TransactionSupplierTest
Test: atest WMShellUnitTests:WindowSessionSupplierTest
Test: atest WMShellUnitTests:LetterboxGestureDelegateTest

Change-Id: I1dea67855d5194d5c66e8c1a4d118a9c1f3cce2c