MessageCore::StringUtil::replacePrefixes: add unit tests

Should help with the upcoming port of QRegExp to QRegularExpression.
1 job for !7 with work/ahmad/qre-stringutil-unit-tests in 31 minutes and 2 seconds (queued for 98 minutes and 25 seconds)
detached
Status Job ID Name Coverage
  Build
passed #62038
linux kf5-qt5 qt5.12

00:31:02

35.0%