SF: Fix a race between layer creation and apply transaction

Between commitCreatedLayers and applyTransactions in the main
thread, the client could create a new layer and queue a transaction.
This will mean a layer transaction can be applied before the layer
can be committed.

Fix this by flushing the transactions to be applied before
committing any new layers.

Test: presubmit
Fixes: b/262336014

Change-Id: Id2848af4fbb7afe4e6a20a48f6a8a13f322e1cd7