The lack of this was hidden by other rules (redundant with it) until
CLDR v45, but v46 prunes the redundant rules, breaking this. So
include the missing rule and tweak the code that assumed likely
sub-tag rules preserved language, since this one doesn't. Rework the
tail of withLikelySubtagsAdded() to correctly use this rule, now that
we have it. (The prior comment about there being no match-all was
wrong: CLDR did have it, but our data skipped it.) Amended one test
affected by it (when system locale wasn't en_US).
On picking to 6.8, uiLanguages() needed some coaxing to avoid
duplicate C locale entries in tests of qualified C locale.
Task-number: QTBUG-130877
Change-Id: I2a415b67af4bc8aa6a766bcc1e349ee5bda9f174
Reviewed-by: Mate Barany <mate.barany@qt.io>
(cherry picked from commit 303863170c3ea7d1ee1b7188f507ad432ed3f860)
15189742c8