TemplateParserJob: port QRegExp to QRegularExpression

TemplateParserJobTest::test_makeValidHtml unit test still passes.
1 job for !10 with work/ahmad/qre-templateparserjob in 53 minutes and 3 seconds (queued for 24 minutes and 45 seconds)
detached
Status Job ID Name Coverage
  Build
passed #62320
linux kf5-qt5 qt5.12

00:53:03

35.0%