[Settings] Show language names in their own language (e.g., Español not Spanish)

[jo-spek]

Relates to https://github.com/google/ground-android/issues/2826

Please have languages appear in their own native name (English, Français, Español, Português, Tiếng Việt)

Manual language switch has been made available, which is greatly appreciated! However, languages are shown in the currently selected language, i.e. when current language is Spanish, "English" is shown as "Inglés". Difficult for users that have switched to a wrong language to get back. Most extreme example Vietnamese:

Would you know which one to choose to get back to English?

Ideally also add some clear icon for the language setting, as e.g. Wikipedia's:

[jo-spek]

@kenstershiro, for a language icon we might need Victor's input. Can you assign as you see fit please?

[kenstershiro]

Two parts to this:

1. Update the language names to always be in their native language. Should be a quick update to the translation files - @rfontanarosa could you pick this part up?
2. Add an icon to help understand the 'Select language' option when it's not in your native language - @vittorino This is low priority, especially the second point