Currently QLocale::c().bcp47Name() returns "C" which, according to [BCP47], is
not a valid language tag. In particular it does not conform to the ABNF grammar
in section 2.1 which specifies a minimum length of 2 characters for all language
tags.
[BCP47]: https://tools.ietf.org/html/bcp47
This patch changes the return value to "en" seeing as the documentation for
QLocale::Language states that the C language is identical in behavior to
English.
Task-number: QTBUG-61949
Change-Id: I2a381def8fb7156467e01d105da92bb1f4821204
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
af7e756155