[Qt6] QRegExp is deprecated and removed from Qt core

[Ryan M. L. McFadden]

FYI - details given in: https://doc-snapshots.qt.io/qt6-dev/qtcore-changes-qt6.html#regular-expression-classes.

It looks like QRegularExpression may be a (nearly) drop-in replacement; however, I have not tested this.

The offending line of code is here:

https://bitbucket.org/muonspin/musrfit/src/root6/src/musredit_qt6/musredit/PTextEdit.cpp#lines-2291

[Andreas Suter]

fixed in 44aacfca506b4c60