Add overlay options for no internet notifications

Add an option to display the no internet dialog directly instead of
showing a notification when the notification would have been high
priority (typically when the network was explicitly selected). This is
disabled by default, but allows device manufacturers to use a slightly
more disruptive UX to ensure that the user is aware that the network has
no connectivity, and can take action.

Also add an option to show the same notification as "no internet"
instead of the "partial connectivity" notification. This is also
disabled by default, but allows device manufacturers to use the "no
internet" text if they feel that "partial connectivity" text is hard
to understand for the user.

Bug: 193847396
Test: atest NetworkNotificationManagerTest
Original-Change: https://android-review.googlesource.com/1782433
Merged-In: Ib5bd74d8cf973bf70d373dd63648c178fae0ebae
Change-Id: Ib5bd74d8cf973bf70d373dd63648c178fae0ebae
6 files changed