Modified the regex pattern in KEmailAddress::isValidSimpleAddress()
slightly to make kemailaddresstest pass.
Also the regex pattern to check literal domains e.g. [123.123.123.123]
was wrong; now hopefully fixed. Added a couple of listeral domain rows
to the unit test.
When using \xnn escape sequences in a pattern, if more than two hex digits
are used then we must use \x{...}, see perldocs: https://perldoc.perl.org/perlre.html.
Thanks to dfaure who got Giuseppe D'Angelo (upstream QRegularExpression
author) to take a look at the code.