Support `locale` module on Android

Migrated from https://github.com/chaquo/chaquopy/issues/1150:

From https://github.com/beeware/toga/discussions/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 https://github.com/python/cpython/issues/90371#issuecomment-2991401118.

Inizia con il modulo locale di Python e le indicazioni sul contesto Android collegate nell’issue; non sono indicati file o test specifici. Determina come accedere alla locale corrente di Android e verifica che locale.getlocale() la rifletta invece di restituire sempre en_US, mantenendo la compatibilità con locale.setlocale.