Set starting frame to startTransaction for ActivityEmbedding transition

Before, the first frame is set later when the animation starts, which
can have a flicker between the startTransaction.apply().

Fix: 268309880
Test: deflaky the OpenActivityEmbeddingSecondaryToSplitTest
Change-Id: Iedeb91295ec365e9a82f5b06539d07745ff6d699
2 files changed