Use configured browser locales for date formatting

What does this MR do?

This allows us to decide a little better what a user wants as a locale for using with the Intl browser APIs. If they have set their GitLab to a language, it will check whether navigator.languages contains matching ones. This function always adds en as a fallback in order to have date renders if all fails before it.

• Example one: GitLab language is en and browser languages are: ['en-GB', 'en-US']. We would choose ['en-GB', 'en-US', 'en'] as the preferred locales, the Intl APIs would try to format first as British English, if that isn't available US or any English.
• Example two: GitLab language is en and browser languages are: ['de-DE', 'de']. We would choose ['en'], so the Intl APIs would prefer English formatting in order to not have German dates mixed with English GitLab UI texts. If the user wants for example British English formatting (24h, etc), they could set their browser languages to ['de-DE', 'de', 'en-GB'].
• Example three: GitLab language is de and browser languages are
  ['en-US', 'en']. We would choose ['de', 'en'], aligning German dates with the chosen translation of GitLab.

This function is currently only used for absolute dates:

• !65570 (merged)

Changelog: changed

Screenshots or Screencasts (strongly suggested)

GitLab Language	Browser Locale	Result	Screenshot
en	en	Created May 18, 2021, 3:55 PM
en	en-US	Created May 18, 2021, 3:55 PM
en	en-GB	Created 18 May 2021, 15:55
en	en-AU	Created 18 May 2021, 3:55 pm
de	en-GB	Created 18.05.2021, 15:55

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