[Notif] Implement a min display time of 3sec for pinned-by-user HUNs.

Pinned-by-user HUNs show up when a user taps the status bar notification
chip. Since that's clear user intent, keep that HUN around for at least
3 seconds before showing a new HUN.

Fixes: 388540989
Bug: 364653005
Flag: com.android.systemui.status_bar_notification_chips

Test: Tap promoted notification chip then immediately send a HUNing
notif -> verify promoted notification stays visible for 3 seconds before
new HUN shows up
Test: Spam normal notifications -> verify they still use the old 0.5
second minimum display time
Test: atest HeadsUpManagerImplTest

Change-Id: I2d2c73fd212da636f511bef023e73e7def075154