refactor: consolidate font picking into one dialog (#6531)

Instead of three separate dropdowns in the setting dialog, we now expose a single label + button combo for modifying the font.
When the button is pressed, we open a custom font dialog allowing the user to customize the font family, font size, and font weight.

Reviewed-by: nerix <nerixdev@outlook.de>
Reviewed-by: pajlada <rasmus.karlsson@pajlada.com>

src/widgets/dialogs/font/IntItem.hpp

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <QListWidget>
+#include <QListWidgetItem>
+#include <QString>
+
+namespace chatterino {
+
+class IntItem : public QListWidgetItem
+{
+public:
+    static constexpr int TYPE_ID = QListWidgetItem::UserType + 101;
+
+    IntItem(int v = 0, QListWidget *parent = nullptr);
+
+    /// setText should not be used, we only store int values in this item
+    ///
+    /// use setValue instead.
+    void setText(const QString &) = delete;
+
+    bool operator<(const QListWidgetItem &other) const override;
+
+    void setValue(int v);
+    int getValue() const;
+
+private:
+    int value;
+};
+
+/// Iterate through all items in the given list and return the item
+/// matching the given value
+IntItem *findIntItemInList(QListWidget *list, int value);
+
+}  // namespace chatterino