[Notif] Rename HeadsUpManagerPhoneTest to HeadsUpManagerImplTest.

Once we eventually merge the two HeadsUpManager test files, we want it
to be in Kotlin. Since HeadsUpManagerPhoneTest is in Kotlin, give that
test file the correct name.

Bug: 378142453
Flag: EXEMPT refactor
Test: atest HeadsUpManagerImplOldTest HeadsUpManagerImplTest
Change-Id: I7fd412ba26b20e8ca28b3db1aa43c37973a12412
3 files changed