refactor registering fixes for each rule

[andrew-bekhiet-solid]

Instead of:

void main() {
  final rule = DoubleLiteralFormatRule();
  registry.registerLintRule(rule);
  registry.registerFixForRule(rule.code, DoubleLiteralFormatFix.new);
}

Add and implement an interface that exposes fixesForCodes getter that will return pairs of code and its fix constructor:

void main() {
  final rule = DoubleLiteralFormatRule();
  registry.registerLintRule(rule);
  for (final MapEntry(key: code, value: fixFn) in rule.fixesForCodes) {
    registry.registerFixForRule(code, fixFn);
  }
}