Remove event signaling logic from Launcher to the tests

Instead of throwing the event on the Launcher, now the test listens
to changes in the view tree and when the condition is meet it stops the
waiter.

Bug: 352569050
Bug: 324261526
Test: IntegrationReorderWidgetsTest
Flag: TEST_ONLY
Change-Id: I94596429cb79af6b298281bd5cd4558e919736e2
1 file changed