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.cpp

@@ -0,0 +1,24 @@
+#include "widgets/helper/RegExpItemDelegate.hpp"
+
+#include <QLineEdit>
+
+namespace chatterino {
+
+RegExpItemDelegate::RegExpItemDelegate(QObject *parent,
+                                       QRegularExpression regexp)
+    : QStyledItemDelegate(parent)
+    , regexp_(regexp)
+{
+}
+
+QWidget *RegExpItemDelegate::createEditor(QWidget *parent,
+                                          const QStyleOptionViewItem &option,
+                                          const QModelIndex &index) const
+{
+    auto *editor = new QLineEdit(parent);
+    editor->setValidator(
+        new QRegularExpressionValidator(this->regexp_, editor));
+    return editor;
+}
+
+}  // namespace chatterino