Port the constructor and addData() method to QAnyStringView, but keep
the overloads taking a QByteArray to avoid extra copies when actual
QByteArray is passed. These overlaods need to be Q_WEAK_OVERLOADs, to
avoid ambiguities (e.g. for const char * arguments).
Additionally, add a test to make sure the patch doesn't break parsing
from a QLatin1StringView input.
[ChangeLog][QtCore][QXmlStremReader] Added constructor and addData()
overloads taking QAnyStringView.
Change-Id: I0efaab82a2123271c88407e380f3c67d1099a4a6
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>