Do not start secondary home on display that cannot host tasks

The system server can crash with a SecurityException due to a race
condition when launching a secondary home activity. This crash occurs if
Display.canHostTasks() becomes false, but WindowManager has not yet
received the corresponding onDisplayChanged() event. This CL prevents
the crash by ensuring Display.canHostTasks() is checked before the
launch attempt.

Bug: 438030031
Test: RootWindowContainerTests
Flag: com.android.server.display.feature.flags.enable_display_content_mode_management
Flag: com.android.window.flags.enable_mirror_display_no_activity
Change-Id: I0957cdcef4dfc955d2b2e89d7dad72e29b28c215