Modify conditions of LogicalDisplay#validateCanHostTasksLocked()

Displays that have FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS or
VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR enabled can always host tasks,
regardless of whether the mirroring switch is disabled.

Bug: 424454438
Test: LogicalDisplayTest
Flag: com.android.server.display.feature.flags.enable_display_content_mode_management
Change-Id: I2040f8530cae9bfaae61da766117d9869f1367c4