Add fatal synchronization error hook

[gabriellanata]

This change introduces a setting to trigger a fatal error when a synchronization error is detected. The FATAL_SYNCHRONIZATION flag has precedence over this setting and it does not change the current default behavior.

Reasoning: We're trying to work through many synchronization errors in our app, but this process is going to take a while. In the meantime, we want to prevent new errors from being added to places that don't have them already. Our approach is to enable this setting for tests and provide a way to disable it for specific tests that currently have synchronization issues. One of the things we need for this to be possible is a way to turn this feature on or off easily.