Preselect widget that is long pressed when entering edit mode

Parse the widget key based on the long pressed position; then set the
key as an intent extra on edit widget activity.

Bug: b/318533815
Test: atest CommunalEditModeViewModelTest
Test: atest CommunalInteractorTest
Flag: ACONFIG com.android.systemui.communal_hub DEVELOPMENT
Change-Id: Ia6effa53374a516f9c7bfab7781788c1b76459b9