Normalize LANG / LC_* environment

This ensures that the current locale supports UTF-8, and that we're
getting a consistent (but still supported by the system) locale for
every configuration except user-facing messages. This should eliminate
any reproducibility problems around sorting, formatting, etc for all
built products, while still showing localized error messages where
available.

Bug: 71573630
Test: LANG=es_ES LANGUAGE=es: m   (check env in soong.log)
Change-Id: If33311899eaed8c44573113ee35c5a71cee503a0