Add card completion popups to chats and search fields

Completes @mention and [[card]] in chat, and card names in the deck
editor, EDHREC, Archidekt, card art rules, and user card settings
searches. Pops up an Arena-style list with mana pips and a card image
preview, flipping the list order when the popup opens above the text
field.

Took 5 minutes

Took 56 seconds

Took 4 minutes

Took 6 minutes

cockatrice/src/interface/widgets/utility/card_completer_styler.h

@@ -0,0 +1,65 @@
+/**
+ * @file card_completer_styler.h
+ * @ingroup UtilityWidgets
+ */
+//! \todo Document this file.
+
+#ifndef CARD_COMPLETER_STYLER_H
+#define CARD_COMPLETER_STYLER_H
+
+#include <QModelIndex>
+#include <QObject>
+
+class CardInfoPictureEnlargedWidget;
+class QCompleter;
+class QKeyEvent;
+class QPoint;
+class ReversedCompleterModel;
+
+/**
+ * @brief Applies styled row painting and a card-image preview to a card completer.
+ *
+ * The completer popup rows are painted by CardCompleterDelegate and the image of
+ * the currently selected (or hovered) row is shown beside the popup.
+ */
+class CardCompleterStyler : public QObject
+{
+    Q_OBJECT
+public:
+    /**
+     * @brief Styles @p completer and follows its current selection.
+     *
+     * The styler is parented to the completer so it lives exactly as long as the
+     * completer itself.
+     */
+    static void apply(QCompleter *completer);
+
+protected:
+    bool eventFilter(QObject *obj, QEvent *ev) override;
+
+private slots:
+    void updatePreview(const QModelIndex &index);
+    void updatePreviewFromHover(const QPoint &pos);
+    void onCompletionReset();
+
+private:
+    explicit CardCompleterStyler(QCompleter *completer, QObject *parent = nullptr);
+
+    void showPreview();
+    void hidePreview();
+    void reposition();
+
+    void updateOrientation();
+    void ensureClosestSelected();
+
+    bool handlePopupKeyPress(QKeyEvent *event);
+    bool isPopupAboveWidget() const;
+
+    QCompleter *completer;
+    ReversedCompleterModel *reversedModel;
+    CardInfoPictureEnlargedWidget *preview;
+    QModelIndex previewedIndex;
+    bool above;
+};
+
+#endif // CARD_COMPLETER_STYLER_H