Helper to verify ui event has bubble info

Create a custom Subject implementation to verify that FakeUiEvent
includes the correct fields from a Bubble.
Allows us to verify bubble data with one call vs checking 3 fields in
every test.

Bug: 349845968
Test: atest BubbleBarExpandedViewTest
Test: atest UiEventSubjectTest
Flag: EXEMPT test only
Change-Id: I16e452b6480bd84a2e1a62e011e67950a6417a4a