Also add a test for the return object of getCanonicalLocaleList().

See https://github.com/tc39/test262/issues/745 for more details.

BUG=v8:5012
TEST=test262/intl402/Intl/getCanonicalLocales/*
TEST=intl/general/getCanonicalLocales

Review-Url: https://codereview.chromium.org/2239523002
Cr-Commit-Position: refs/heads/master@{#38733}