Replace virtual display with simulated display in OpenAppWithExternalDisplayConnected

This CL replaces a virtual display with a simulated display in
OpenAppWithExternalDisplayConnected.
This utility Rule class was recently introduced; a simulated display
offers a better simulation for an physical external display than a
virtual display.

Flag: com.android.window.flags.enable_display_windowing_mode_switching
Bug: 407857271
Test: atest WMShellFlickerTestsDesktopMode:com.android.wm.shell.flicker.OpenAppWithExternalDisplayConnected
Change-Id: I639324377472d2e5562d4158da9665a522c7204c