Add first frame timestamps to AppStartInfo

Logging same value used by StatsD for TTFF for consistency.

Adds a new call into AMS to allow the caller to supply a uid/pid and avoid enforcement against isolated callers.

Test: start several apps, ensure timestamp is added correctly
Bug: 287153617
Flag: android.app.activity_manager.app_start_info_timestamps
Change-Id: I4d5bd1c53462444a2cca6371361d6f1f25d33b99