Remove QObjectRef in favor of QPointer

[fourtf]

Checklist

• I'm reporting a problem with Chatterino
• I've verified that I'm running the most recent nightly build or stable release
• I've looked for my problem on the wiki
• I've searched the issues and pull requests for similar looking reports

Describe your issue

We have a class called QObjectRef which is a pointer to a QObject which is reset when the referenced object is destroyed. It looks, however, like Qt itself has an equivalent class called QPointer. https://doc.qt.io/qt-6/qpointer.html

We can replace the QObjectRef usages and remove the class.

Screenshots

No response

OS and Chatterino Version

Chatterino 2.4.4