Add verbose logging for app image startup cache feature

Will be parsed from logcat to test the feature.
Logging is of the form: AppImage:load_startup_cache

Bug: 124437687
Bug: 123524494

Test: adb shell device_config put runtime_native use_app_image_startup_cache true
Test: start app
Test: look at logcat
Test: repeat with false

Change-Id: I130ef9e6e4b8cb03497c25cd0a88727d5e60ffbc