Add button to thread to reply

![image](/uploads/bf2b6857f797480b429db02c5d01a4f7/image.png){width=254 height=147}

src/timeline/CMakeLists.txt

@@ -46,6 +46,7 @@ ecm_add_qml_module(timeline GENERATE_PLUGIN_SOURCE
         PollComponent.qml
         QuoteComponent.qml
         ReplyAuthorComponent.qml
+        ReplyButtonComponent.qml
         ReplyComponent.qml
         StateComponent.qml
         TextComponent.qml

src/timeline/MessageComponentChooser.qml

@@ -210,6 +210,14 @@ DelegateChooser {
         }
     }
 
+    DelegateChoice {
+        roleValue: MessageComponentType.ReplyButton
+        delegate: ReplyButtonComponent {
+            room: root.room
+            maxContentWidth: root.maxContentWidth
+        }
+    }
+
     DelegateChoice {
         roleValue: MessageComponentType.Verification
         delegate: MimeComponent {

src/timeline/ReplyButtonComponent.qml

@@ -0,0 +1,50 @@
+// SPDX-FileCopyrightText: 2023 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.Controls as QQC2
+import QtQuick.Layouts
+
+import org.kde.kirigami as Kirigami
+import org.kde.kirigamiaddons.delegates as Delegates
+
+import org.kde.neochat
+import org.kde.neochat.chatbar
+
+/**
+ * @brief A component to show a reply button for threads in a message bubble.
+ */
+Delegates.RoundedItemDelegate {
+    id: root
+
+    /**
+     * @brief The NeoChatRoom the delegate is being displayed in.
+     */
+    required property NeoChatRoom room
+
+    /**
+     * @brief The thread root ID.
+     */
+    required property string threadRoot
+
+    /**
+     * @brief The maximum width that the bubble's content can be.
+     */
+    property real maxContentWidth: -1
+
+    Layout.fillWidth: true
+    Layout.maximumWidth: root.maxContentWidth
+
+    leftInset: 0
+    rightInset: 0
+
+    icon.name: "mail-reply-custom"
+    text: i18nc("@action:button", "Reply")
+
+    onClicked: {
+        root.room.threadCache.replyId = "";
+        root.room.threadCache.threadId = root.threadRoot;
+        root.room.mainCache.clearRelations();
+        root.room.editCache.clearRelations();
+    }
+}