CodeChecker: HTML report lets a crafted finding inject script

The HTML report that plist-to-html, CodeChecker parse --export html and CodeChecker cmd diff --output html generate puts the report message, the checker name and the source file path into a script block through json.dumps. json.dumps does not escape the less-than character, so a closing script tag in any of those three fields ends the script element and what follows is parsed as HTML.

The input author is whoever controls the analysed tree or a third-party result file that report-converter ingests, or who holds PRODUCT_STORE in the cmd diff flow. The viewer is somebody else: docs/jenkins_gerrit_integration.md documents writing the report into Jenkins userContent and posting its URL into a Gerrit review. One caveat worth stating up front is that Jenkins serves userContent under a restrictive CSP that would block an inline handler, so that destination is probably safe as configured. The generated report sets no CSP of its own, so the impact lands wherever it is published without one.