ChatBox: Fix jittery ChatBar

ChatBar animated its implicit height, and there is no way for us to
force it animating on integer values only. It is contained in a Layout
type, and QtQuick.Layouts are known to round up size of their items and
position them on an integer scale. All in all, is caused bottom of chat
bar (action icons row and the whole bottom edge) to flicker during
height animation.

src/qml/Component/ChatBox/ChatBox.qml

@@ -65,9 +65,10 @@ ColumnLayout {
         visible: root.currentRoom.canSendEvent("m.room.message")
 
         Layout.fillWidth: true
-        Layout.minimumHeight: Math.max(Kirigami.Units.gridUnit * 2, implicitHeight + Kirigami.Units.largeSpacing)
+        Layout.minimumHeight: Math.max(Kirigami.Units.gridUnit * 2, Math.round(implicitHeight) + Kirigami.Units.largeSpacing)
         // lineSpacing is height+leading, so subtract leading once since leading only exists between lines.
         Layout.maximumHeight: chatBarFontMetrics.lineSpacing * 8 - chatBarFontMetrics.leading + textField.topPadding + textField.bottomPadding
+        Layout.preferredHeight: Math.round(implicitHeight)
 
         currentRoom: root.currentRoom