Remove QObjectRef in favor of QPointer (#4666)

* replace usage of QObjectRef with QPointer

* delete QObjectRef class

* inlucde QPointer header

* Add changelog entry

* use isNull() instead of ! data()

---------

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/util/QObjectRef.hpp

@@ -1,86 +0,0 @@
-#pragma once
-
-#include <QApplication>
-#include <QObject>
-
-#include <type_traits>
-
-namespace chatterino {
-/// Holds a pointer to a QObject and resets it to nullptr if the QObject
-/// gets destroyed.
-template <typename T>
-class QObjectRef
-{
-public:
-    QObjectRef()
-    {
-        static_assert(std::is_base_of_v<QObject, T>);
-    }
-
-    explicit QObjectRef(T *t)
-    {
-        static_assert(std::is_base_of_v<QObject, T>);
-
-        this->set(t);
-    }
-
-    QObjectRef(const QObjectRef &other)
-    {
-        this->set(other.t_);
-    }
-
-    ~QObjectRef()
-    {
-        this->set(nullptr);
-    }
-
-    QObjectRef &operator=(T *t)
-    {
-        this->set(t);
-
-        return *this;
-    }
-
-    operator bool()
-    {
-        return t_;
-    }
-
-    T *operator->()
-    {
-        return t_;
-    }
-
-    T *get()
-    {
-        return t_;
-    }
-
-private:
-    void set(T *other)
-    {
-        // old
-        if (this->conn_)
-        {
-            QObject::disconnect(this->conn_);
-        }
-
-        // new
-        if (other)
-        {
-            // the cast here should absolutely not be necessary, but gcc still requires it
-            this->conn_ =
-                QObject::connect((QObject *)other, &QObject::destroyed, qApp,
-                                 [this](QObject *) {
-                                     this->set(nullptr);
-                                 },
-                                 Qt::DirectConnection);
-        }
-
-        this->t_ = other;
-    }
-
-    std::atomic<T *> t_{};
-    QMetaObject::Connection conn_;
-};
-}  // namespace chatterino