Please add locale-specific toUpper/LowerCase

[robertoscaramuzzi]

Currently in our project we need to have separate Intl.messages for messages such as 'Paused' and 'PAUSED' because calling Intl.message('Paused').toUpperCase() might be wrong in some languages, namely Turkish, Azeri and Lithuanian.

This introduces the risk that the two messages might be translated differently, introducing confusion for the user.

Note that Intl has toBeginningOfSentenceCase that handles Turkish and Azeri (but not Lithuanian) so this doesn't seem like such a leap.

See http://hg.openjdk.java.net/jdk9/jdk9/jdk/file/65464a307408/src/java.base/share/classes/java/lang/ConditionalSpecialCasing.java

for the OpenJDK implementation (or don't look at it if there are intellectual property issues).