[Status bar] Use a real view in tests

CollapsedStatusBarFragmentTest was using a mocked notification area
inner view, which means that all of the assertions had to be done as
`verify` calls. This CL addresses a comment that suggested we use a real
view, and allows for more fine-grained testing of that view for the next
CL

Test: CollapsedStatusBarFragmentTest
Bug: 302168270
Flag: NONE
Change-Id: I2f15cac0cc329f6b42506298b8141df2e8882b61