bool Q{String*,ByteArra}::compareEquals(..., Qt::CaseSensitivity)

As discussed in https://codereview.qt-project.org/c/qt/qtbase/+/515584/1/src/plugins/platforms/ios/qiosintegration.mm#303, when doing case insensitive compares it's akward to have to use compare() == 0, and there is a non-zero risk of forgetting the == 0 part, leading to the wrong logic.

Just like startsWith(), it would be nice with a more straight forward API that would lead to user code along the lines of:

if (foo.compareEquals(bar, Qt::CaseInsensitive))