Allow opting out of delegate generation

[denist11]

Many users of this package may want to create their own LocalizationDelegate<T> implementation and provide their own localized resource T.
The reason for this, I have noticed, is often related to the way the delegate is initialized, not allowing more than one delegate to be used at a time.

However, this is often necessary, for example when a package wants to take advantage of the convenience of using this generator to provide its localizations.

One possible solution would be to add a configuration in the pubspec.yaml such as:

flutter_intl:
  enabled: true
  skip_delegate: true # Optional

And avoid generating l10n.dart when this option is enabled. This way the user can build his own initialization mechanism according to their needs.

I currently removed all dependencies to this generator, and opted to use intl_translation directly:

$ dart run intl_translation:generate_from_arb \
          --output-dir=path/to/intl \
          path/to/app_localizations.dart \
          path/to/arb/intl_*.arb

I don't have time to work on a PR and the solution I found seems convenient enough to abandon intl_utils for my use case. I hope though that in the future this request will be taken into consideration and someone will decide to work on it.

Related Issues

• #95
• #31