DateFormatTest: fix after ICU upgrade

* Timezone names have changed. Test the medium time format which doesn't
include them, as we aren't forcing a specific one.
* French date format also changed to use 4 digit year name.
Add BMessageFormat class.

This can be used to format complex messages properly. It moves the
complexity of handling plural forms, gender, and anything else needed
into the localizable string, rather than hardcoding it in the code.

This moves the difficulty of handling these things properly to people
doing translations, rather than relying on developers to do it.

Fixes #10755, but our localization must now be updated to make use of
the feature.
Start making use of BMessageFormat.
Fix singular for Processor count.