[libc++][ci] Installs Japanese locale in Docker.

The alternative outputs of std::put_time and std::strftime are the
easiest to test with the Japanese locale. This is a preparation for the
tests of the chrono formatters.

Note since it takes a while before the Docker file changes propagate to
the build nodes the verification of the locale is done in a separate
patch.

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D122736