Language tags with Unicode extensions can have multiple subtags
for a key (e.g. -ca-ismalic-civil has 'islamic-civi' for 'ca').

BUG=v8:4749
TEST=intl/date-format/calendar-with-multiple-type-subtags.js

Review-Url: https://codereview.chromium.org/2248563003
Cr-Commit-Position: refs/heads/master@{#38692}