Fixing flakiness of KeyboardTouchpadTutorialViewModelTest

Test was sometimes failing because of using LifecycleRegistry with provided LifecycleOwner - owner is held by registry by WeakReference only. Because it wasn't referenced anywhere else, sometimes it would be garbage collected before our `lifecycle.handleLifecycleEvent()` calls.
Instead let's just call lifecycle methods directly to avoid using lifecycle-related objects and depend on them.
More info in b/376676384

Fixes: 376676384
Test: KeyboardTouchpadTutorialViewModelTest with added System.gc() calls
Flag: EXEMPT test fix
Change-Id: I3605396e2deb8f9dcdf8eab5ad87fb34ab8cc9f3