Add support for IntlMessageFormatter

[welcoMattic]

In anticipation of Symfony 4.2 release, we should work on support of the new IntlMessageFormatter

See https://symfony.com/blog/new-in-symfony-4-2-intlmessageformatter

I'm looking for all changes involved by this new Formatter

[Nyholm]

What is needed from the bundle's side to support this?

[welcoMattic]

I totally forgot that I opened this issue over a year ago. I'm sorry. I'll get back to it and figure out what we need to do to support IntlMessageFormatter as soon as I can.

[odolbeau]

I'm already using this format in my app & everything looks fine, even if I didn't try to use a translation as complicated as the one given in the example.

[welcoMattic]

As I see, and test in a real life application, there's nothing to do to support this format but improve Profiler message editor (which is a dead simple textarea). May be we should look around https://format-message.github.io/icu-message-format-for-translators/editor.html?

[bocharsky-bw]

Should be fixed in #452