Convert TimelineDelegate to cpp

There are 2 main reason for doing this:
1. Because I can, I wanted to see if I could do it
2. It gets rid of the janky qml re parenting stuff so should be faster.

src/timeline/timelinedelegate.h

@@ -0,0 +1,99 @@
+// SPDX-FileCopyrightText: 2024 James Graham <james.h.graham@protonmail.com>
+// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+
+#ifndef TIMELINEDELEGATE_H
+#define TIMELINEDELEGATE_H
+
+#include <QQuickItem>
+
+#include <Kirigami/Platform/Units>
+
+/**
+ * @brief The base Item for all delegates in the timeline.
+ *
+ * This component handles the placing of the main content for a delegate in the
+ * timeline. The component is designed for all delegates, positioning them in the
+ * timeline with variable padding depending on the window width.
+ *
+ * This component also supports always setting the delegate to fill the available
+ * width in the timeline, e.g. in compact mode.
+ */
+class TimelineDelegate : public QQuickItem
+{
+    Q_OBJECT
+    QML_ELEMENT
+
+    /**
+     * @brief This property holds the visual content Item.
+     *
+     * It will be resized both in width and height with the layout resizing.
+     * Its height will be resized to still have room for the heder and footer
+     */
+    Q_PROPERTY(QQuickItem *contentItem READ contentItem WRITE setContentItem NOTIFY contentItemChanged FINAL)
+
+    /**
+     * @brief Whether the contentItem should fill all available width regardless of how wide the delegate is.
+     *
+     * The left and right padding values will still be respected.
+     */
+    Q_PROPERTY(bool alwaysFillWidth READ alwaysFillWidth WRITE setAlwaysFillWidth NOTIFY alwaysFillWidthChanged FINAL)
+
+    /**
+     * @brief The minimum padding to the left of the content.
+     */
+    Q_PROPERTY(qreal leftPadding READ leftPadding WRITE setLeftPadding NOTIFY leftPaddingChanged FINAL)
+
+    /**
+     * @brief The minimum padding to the right of the content.
+     */
+    Q_PROPERTY(qreal rightPadding READ rightPadding WRITE setRightPadding NOTIFY rightPaddingChanged FINAL)
+
+public:
+    TimelineDelegate(QQuickItem *parent = nullptr);
+
+    [[nodiscard]] QQuickItem *contentItem();
+    void setContentItem(QQuickItem *item);
+
+    [[nodiscard]] bool alwaysFillWidth();
+    void setAlwaysFillWidth(bool alwaysFillWidth);
+
+    [[nodiscard]] qreal leftPadding();
+    void setLeftPadding(qreal leftPadding);
+
+    [[nodiscard]] qreal rightPadding();
+    void setRightPadding(qreal rightPadding);
+
+Q_SIGNALS:
+    void contentItemChanged();
+    void alwaysFillWidthChanged();
+    void leftPaddingChanged();
+    void rightPaddingChanged();
+
+protected:
+    void geometryChange(const QRectF &newGeometry, const QRectF &oldGeometry) override;
+    void componentComplete() override;
+
+private:
+    Kirigami::Platform::Units *m_units = nullptr;
+    void setCurveValues();
+
+    qreal m_leftPadding;
+    qreal m_rightPadding;
+
+    qreal m_startBreakpoint;
+    qreal m_endBreakpoint;
+    int m_startPercentWidth = 100;
+    int m_endPercentWidth = 85;
+    qreal m_maxWidth;
+    int availablePercentageWidth() const;
+    qreal maxAvailableWidth() const;
+    qreal availableWidth() const;
+    bool m_alwaysFillWidth = false;
+
+    void resizeContent();
+    void updateImplicitHeight();
+
+    QPointer<QQuickItem> m_contentItem;
+};
+
+#endif