feat(StringUtils): implement `plainText(htmlFragment)`

- converts an HTML fragment to plain text
- move the impl to C++ so that it can be used directly from QML too

ui/StatusQ/include/StatusQ/stringutilsinternal.h

@@ -19,6 +19,8 @@ public:
 
     Q_INVOKABLE QString extractDomainFromLink(const QString& link) const;
 
+    Q_INVOKABLE QString plainText(const QString& htmlFragment) const;
+
 private:
     QQmlEngine* m_engine{nullptr};
 };

ui/StatusQ/src/StatusQ/Core/Utils/StringUtils.qml

@@ -16,4 +16,8 @@ QtObject {
     function extractDomainFromLink(link) {
         return Internal.StringUtils.extractDomainFromLink(link)
     }
+
+    function plainText(htmlFragment) {
+        return Internal.StringUtils.plainText(htmlFragment)
+    }
 }

ui/StatusQ/src/stringutilsinternal.cpp

@@ -5,6 +5,7 @@
 #include <QQmlEngine>
 #include <QQmlFileSelector>
 #include <QUrl>
+#include <QTextDocumentFragment>
 
 StringUtilsInternal::StringUtilsInternal(QQmlEngine* engine, QObject* parent)
     : m_engine(engine)
@@ -73,3 +74,8 @@ QString StringUtilsInternal::extractDomainFromLink(const QString& link) const
     }
     return url.host();
 }
+
+QString StringUtilsInternal::plainText(const QString &htmlFragment) const
+{
+    return QTextDocumentFragment::fromHtml(htmlFragment).toPlainText();
+}