Codesigning Script

This script will--given a particular Flutter Engine revision--fetch the necessary cache artifacts and codesign & notarize them. Pre-requisites are:

1. You must have gsutil installed and authenticated to write to the flutter-infra bucket.
2. The following env variables must be set: CODESIGN_USERNAME, CODESIGN_CERT_NAME, APP_SPECIFIC_PASSWORD. There is an internal doc that has more information on these.
3. Xcode must be installed, and a Developer ID certificate must be present in the keychain (the name of this cert should be CODESIGN_CERT_NAME)

Usage is as follows:

./codesign.py <engine_revision_hash>