[Tools] Add ability to validate recursive ICU messages

[LeanidShutau]

We need to parse nested ICU messages, example:

intl.formatMessage(
  {
    id: 'xpack.beatsManagement.beats.removedNotificationDescription',
    defaultMessage:
      'Removed tag {tag} from {assignmentsLength, plural, one {beat {beatName}} other {# beats}}.',
  },
  {
    tag: 'tagValue',
    assignmentsLength: 'assignmentsLengthValue',
    beatName: 'beatNameValue',
  }
);

Currently beatName reference is ignored.

ICU messages parser in i18n_check tool should parse ICU messages recursively.

[elasticmachine]

Pinging @elastic/kibana-platform

[azasypkin]

@LeanidShutau can you please add more details to the issue description? I suspect it's something related to what we've been discussing recently but can't match title to anything I am aware of.

[LeanidShutau]

@LeanidShutau can you please add more details to the issue description? I suspect it's something related to what we've been discussing recently but can't match title to anything I am aware of.

Of course. TODO means that I'm planning to update the description. I just didn't have time to do that, but also didn't want to forget about the task.