Don't include a flyout for BubbleInfo object if we shouldn't show it

There's no notion of not showing the flyout for bubble bar, but there
are cases where it shouldn't be shown (e.g. DND).

Simply don't add the flyout message to the BubbleInfo object if we
shouldn't show it.

Flag: com.android.wm.shell.enable_bubble_bar
Test: atest BubbleTest
Test: - turn on DND mode with bubble bar, get a notification, observe
        that the flyout doesn't show (but the dot is there)
Bug: 444398581
Change-Id: I7daa232f1b25ef2d497dd95e2e0d34cd1fdc686d