Let Ctrl+A cause a key event with text Ctrl+A (0x01), like we do on
the other platforms. Previously we would use 'A', which would confuse
some applications.

Task-number: QTBUG-50398
Change-Id: Ie3def4bd9c96e538b2572b88fae029d347e08814
Reviewed-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>