set locale normalizes localeName while getOrCreateIntl does not

[dagroe]

• I am on the latest ember-intl version
• I have searched the issues of this repo and believe that this is not a duplicate

Environment

• Ember Version: 3.28.9
• Ember CLI Version: 4.5.0
• Ember Intl Version: 6.0.0-beta.3
• Browser(s): Chrome 103.0.5060.134
• Node Version: 12.14.1

Steps to Reproduce

My browsers locale is set to de-DE. I am setting the locales on the intl service as

this.intl.setLocale(['de-DE', 'en-gb']);

During setLocale(locale) the following happens:

setLocale(locale) {
  (true && !(locale) && (0, _debug.assert)(`[ember-intl] no locale has been set!  See: https://ember-intl.github.io/ember-intl/docs/quickstart#4-configure-ember-intl`, locale));
  this.locale = locale;
  this.getOrCreateIntl(locale);
}

Via this.locale = locale the setter is called, which normalizes the passed locales and sets this._locale = ['de-de', 'en-gb'].
Then getOrCreateIntl creates the intl but doesn't normalize de-DE to de-de, which creates an entry in this._intls under key de-DE.

Now if I translate via the t helper in a template, in serviceFormatterProxy the locale is set via this.locale is set to ['de-de', 'en-gb'] (via this._locale).
However, intl = this.getIntl(locale); sets intl to undefined since there is no entry for de-DE in this._intls.

As a consequence, the format method in FormatMessage throws an error since intl is undefined.

Happens only in chrome when language is set to German.