Consistent localized formatting

[mary-ext]

Just realized Lingui offers convenience methods for language-aware number and date-time formatting via i18n.number() and i18n.date() respectively.

This pull request switches most of our formatting to use that, except for the ago function, I'll touch on that in a separate pull request (haven't figured out how to make unit formatting for months and minutes to not be the same m suffix, I think we might need a separate logic for English, unfortunately)

This seems like the better approach because currently we're very inconsistent as to how we're dealing with localized formatting. Here's how we've been doing it so far:

• pass undefined as the locale
• pass locale retrieved from expo-localization
• pass locale from our content language settings
• enforce en-US locale

I've removed the formatCountShortOnly function as it's only used in the drawer, I'm not sure why it should be using a different formatting than the one in <Metrics> component, but we can add that back if necessary.

[mary-ext]

I've just noticed that some locales doesn't seem to have any compact notation formatting for thousands specifically, like German and Italian, I'm not sure what to do in this case, should we do a fallback to English in those scenarios? or should we just let it be?

English	German

[mary-ext]

I feel like there's a better way to do this (where we have different styling for count and suffix) in a way that's more i18n-friendly (doesn't assume spacing and prefix/suffix)

{count, plural,
  one {# <0>post</0>}
  other {# <0>posts</0>}
}

Problem is, I don't understand ICU MessageFormat enough to know if there's like, a way to actually format the number. Perhaps this works as an alternative?

{count, plural,
  one {{fixedCount} <0>post</0>}
  other {{fixedCount} <0>posts</0>}
}

This isn't much of a priority right now though, just food for thought.

[tkusano]

In Japanese, i18n.number() defines an compact notation for numbers in tens of thousands, but does not seem to define for numbers in thousands. I think it's fine to leave it as it is, without falling back to English.