StringUtil: Port QRegExp to QRegularExpression

stringutil unit test still passes.
2 jobs for master in 82 minutes and 24 seconds (queued for 28 minutes and 7 seconds)
Status Job ID Name Coverage
  Build
passed #62436
build_clazy_clang_tidy

00:55:42

passed #62435
linux kf5-qt5 qt5.12

00:34:21

35.0%