Support `locale` module on Android

[mhsmith]

Migrated from chaquo/chaquopy#1150:

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From beeware/toga#2562:

Hello, how can I recognize the current language with locale.getlocale()?
When i try it on android, it only returns ('en_US', 'UTF-8'), even if default language was set to an other language.

I don't think Android sets any of the standard LC_... environment variables, probably because it supports changing the locale within the lifetime of a single process. Instead, it provides an Android-specific API:

context.getResources().getConfiguration().getLocales().get(0)

This will return a string in the form en_US, which can be passed to locale.setlocale.

The difficult part is getting a reference to the context object. For details, see #90371 (comment).