TemplateParserJob: port QRegExp to QRegularExpression

TemplateParserJobTest::test_makeValidHtml unit test still passes.
2 jobs for master in 58 minutes and 6 seconds (queued for 29 minutes and 6 seconds)
Status Job ID Name Coverage
  Build
passed #62322
build_clazy_clang_tidy

00:57:33

passed #62321
linux kf5-qt5 qt5.12

00:44:36

35.0%