Initialize ProtoLog once on first activity launch

Fixes an IllegalStateException crash caused by using ProtoLog before it
was initialized. This could happen in UI processes where logging code
was called during the activity lifecycle before ProtoLog.start() was
invoked.

This change moves the initialization to handleLaunchActivity(), ensuring
it runs in processes that have a UI. A static boolean,
sProtoLogInitialized, is used to guarantee that the initialization
occurs only once per process, on the first activity launch.

The ProtoLog initialization here will be guarded by a flag to roll out
gradually and safely.

Bug: 432646252
Flag: android.tracing.imetracker_protolog
Change-Id: Ia9160a26702550d7bc7ef6a0c2e1e7e4f4cdf490