src: default --icu_case_mapping on as a v8 option

* toLocaleUpperCase() and toLocaleLowerCase() do not function properly
without this flag.
* basic test case. The test case would fail if `--no_icu_case_mapping`
was set.

Fixes: https://github.com/nodejs/node/issues/9445
PR-URL: https://github.com/nodejs/node/pull/9454


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>