Don't send split info callback before activity is created

Sending a split info callback before activity created would
give developer a reference to a not fully initalized class.
It is possible that an attemp to apply actions to such an
activity in the split callback would lead to unexpected
issues for developers. E.g. one might assuming that the
UI for an activity would've been constructed at this point
and try to update it to fit the split or collapsed state
requirements.

Bug: 228770009
Test: atest CtsWindowManagerJetpackTestCases:ActivityEmbeddingLifecycleTests
Change-Id: I3a19a028ad6da9a6d534a97d315bce5f95b191af