Bubble API: Allow developers to create BubbleMetadata from a shortcut id

Adds an option to specify a bubble via a shortcutId. If the builder had
icon / intent previously specified, the shortcutId will clobber those
and vice versa.

Unfortunately, this means that BubbleMetadata#getIcon and #getIntent may
return null when previously they were non-null. I've deprecated these
getters and introduced new ones along with new setters so that the naming
remains consistent.

NoMan will check if that shortcut exists before applying FLAG_BUBBLE.

Update SystemUI to use BubbleMetadata builder with shortcut id for the
shortcut experiment.

Adds test to ensure the launcher apps callback is added / removed
appropriately & that notifs with shortcut bubbles are properly flagged
or unflagged.

Test: atest NotificationManagerServiceTest
Test: atest NotificationTest NotificationManagerTest (see CTS CL)
Bug: 138116133
Bug: 144352570
Change-Id: I2e8155edc7fd70d6978fc80310f071bf6510e0d2