Split message content into its own module

This is laying some groundwork for the rich text chatbar.

src/messagecontent/ItineraryReservationComponent.qml

@@ -0,0 +1,46 @@
+// 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
+
+import QtQuick
+import QtQuick.Layouts
+
+import org.kde.kirigami as Kirigami
+import org.kde.kirigamiaddons.formcard as FormCard
+
+/**
+ * @brief A base component for an itinerary reservation.
+ */
+FormCard.FormCard {
+    id: root
+
+    /**
+     * @brief An item with the header content.
+     */
+    property alias headerItem: headerDelegate.contentItem
+
+    /**
+     * @brief An item with the main body content.
+     */
+    property alias contentItem: content.contentItem
+
+    Layout.fillWidth: true
+    implicitWidth: Math.max(headerDelegate.implicitWidth, content.implicitWidth)
+
+    Component.onCompleted: children[0].radius = Kirigami.Units.cornerRadius
+
+    FormCard.AbstractFormDelegate {
+        id: headerDelegate
+        Layout.fillWidth: true
+        background: Rectangle {
+            color: Kirigami.Theme.backgroundColor
+            Kirigami.Theme.colorSet: Kirigami.Theme.Header
+            Kirigami.Theme.inherit: false
+        }
+    }
+    FormCard.AbstractFormDelegate {
+        id: content
+        Layout.fillWidth: true
+        background: null
+    }
+}
+