[33/n] Consider IME test only for Legacy Letterbox Surfaces

At the moment the Letterbox implementation in Shell doesn't
recognise changes in orientation when done invoking
Activity#setRequestedOrientation().

Flag: com.android.window.flags.app_compat_refactoring
Bug: 409043134
Test: atest FlickerTestsIme:OpenImeWindowToFixedPortraitAppTest

Change-Id: I629a1525c7ed6aefc7b8ebc7e13e182562cd8f1b