Adds licenses to the registry.
To avoid actually manipulating the licenses unless strictly necessary, licenses are added by adding a closure that returns a list of LicenseEntry objects. The closure is only called if licenses is itself called; in normal operation, if the user does not request to see the licenses, the closure will not be called.
Source
static void addLicense(LicenseEntryCollector collector) {
_collectors ??= <LicenseEntryCollector>[];
_collectors.add(collector);
}