StringUtil: Port QRegExp to QRegularExpression

stringutil unit test still passes.
1 job for !8 with work/ahmad/qre-stringutil in 54 minutes and 37 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Build
passed #62434
linux kf5-qt5 qt5.12

00:54:37

35.0%