Cherrypick Other user read markers 23.04

Add the ability to see other user's read markers. 

![image](/uploads/a4bdc35a60ab10685c7d3ea4d9b13c87/image.png)

Implements network/neochat#133


(cherry picked from commit 23303c0483)

src/qml/Component/Timeline/AvatarFlow.qml

@@ -0,0 +1,37 @@
+// SPDX-FileCopyrightText: 2022 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 2.15
+import QtQuick.Controls 2.15 as QQC2
+
+import org.kde.kirigami 2.15 as Kirigami
+
+Flow {
+    id: root
+
+    property var avatarSize: Kirigami.Units.iconSizes.small
+    property alias model: avatarFlowRepeater.model
+    property string toolTipText
+
+    spacing: -avatarSize / 2
+    Repeater {
+        id: avatarFlowRepeater
+        delegate: Kirigami.Avatar {
+            implicitWidth: avatarSize
+            implicitHeight: avatarSize
+
+            name: modelData.displayName
+            source: modelData.avatarMediaId ? ("image://mxc/" + modelData.avatarMediaId) : ""
+            color: modelData.color
+        }
+    }
+
+    QQC2.ToolTip.text: toolTipText
+    QQC2.ToolTip.visible: hoverHandler.hovered
+    QQC2.ToolTip.delay: Kirigami.Units.toolTipDelay
+
+    HoverHandler {
+        id: hoverHandler
+        margin: Kirigami.Units.smallSpacing
+    }
+}

src/qml/Component/Timeline/StateDelegate.qml

@@ -134,5 +134,12 @@ QQC2.Control {
             folded = !folded
             foldedChanged()
         }
+        AvatarFlow {
+            Layout.alignment: Qt.AlignRight
+            Layout.rightMargin: Kirigami.Units.largeSpacing
+            visible: showReadMarkers
+            model: readMarkers
+            toolTipText: readMarkersString
+        }
     }
 }

src/qml/Component/Timeline/TimelineContainer.qml

@@ -338,6 +338,13 @@ ColumnLayout {
 
         visible: eventType !== MessageEventModel.State && eventType !== MessageEventModel.Notice && reaction != undefined && reaction.length > 0
     }
+    AvatarFlow {
+        Layout.alignment: Qt.AlignRight
+        Layout.rightMargin: Kirigami.Units.largeSpacing
+        visible: showReadMarkers
+        model: readMarkers
+        toolTipText: readMarkersString
+    }
 
     function isVisibleInTimeline() {
         let yoff = Math.round(y - ListView.view.contentY);