Review and tag src/gui/text/qcssparser.cpp src/gui/text/qtexthtmlparser.cpp src/gui/text/qtextmarkdownimporter.cpp

This task is about reviewing the different parsers our text handling code uses (HTML, markdown, css).

The task is to review all code mentioned in the task title for the presence of code that is considered security-critical, according to https://contribute.qt-project.org/quips/23. In particular, we are looking for parsers that touch untrusted data directly. Such code should have the security header

// Qt-Security score:critical reason:data-parser

Definition of done:
1. All code mentioned in the task header is reviewed
2. If security critical code is found, the header is added.