Prevent user from entering incorrect characters in Live Notifications channels list (#3715)

Co-authored-by: Sidd <iProdigy@users.noreply.github.com>
Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/widgets/helper/RegExpItemDelegate.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <QRegularExpression>
+#include <QStyledItemDelegate>
+
+namespace chatterino {
+
+class RegExpItemDelegate : public QStyledItemDelegate
+{
+    Q_OBJECT
+
+public:
+    RegExpItemDelegate(QObject *parent, QRegularExpression regexp);
+
+    QWidget *createEditor(QWidget *parent, const QStyleOptionViewItem &option,
+                          const QModelIndex &index) const override;
+
+private:
+    const QRegularExpression regexp_;
+};
+
+}  // namespace chatterino