Update Locale.getISOLanguages() javadoc

Android supports the ISO 639-2 standard. The API behavior diverges from
OpenJDK because the languages with 3-letter ISO 639 code are widely used
and can be set as a System language on Android. Returning 2-letter codes
only excludes some languages and isn't useful for developers.

Bug: 277929411
Test: treehugger
Change-Id: If6a05607cf73f6f73a138065c591a50cdb75e798
1 file changed