Fix copying multi-line selected rich text

For rich text (rendered HTML) fields and areas, the selectedText
property for some reason contains "\u2028" or "\u2029"
characters that look like newlines in Qt programs but are just
invisible anywhere else. Translate them to normal "\n".

src/gui/Pages/Chat/Composer/MessageArea.qml

@@ -225,7 +225,7 @@ HTextArea {
         if (ev.text && autoCompletionOpen) acceptAutoCompletion()
 
         if (ev.matches(StandardKey.Copy) &&
-            ! area.selectedText &&
+            ! area.selectedPlainText &&
             eventList &&
             (eventList.selectedCount || eventList.currentIndex !== -1))
         {
@@ -237,7 +237,7 @@ HTextArea {
         // FIXME: buggy
         // if (ev.modifiers === Qt.NoModifier &&
         //     ev.key === Qt.Key_Backspace &&
-        //     ! area.selectedText)
+        //     ! area.selectedPlainText)
         // {
         //     ev.accepted = true
         //     area.remove(

src/gui/Pages/Chat/Timeline/EventContent.qml

@@ -82,7 +82,7 @@ HRowLayout {
             window.settings.maxMessageCharactersPerLine
         )
 
-    readonly property alias selectedText: contentLabel.selectedText
+    readonly property alias selectedText: contentLabel.selectedPlainText
 
 
     spacing: theme.chat.message.horizontalSpacing
@@ -182,9 +182,9 @@ HRowLayout {
             Layout.maximumWidth: eventContent.maxMessageWidth
             Layout.fillWidth: true
 
-            onSelectedTextChanged: if (selectedText) {
+            onSelectedTextChanged: if (selectedPlainText) {
                 eventList.delegateWithSelectedText = model.id
-                eventList.selectedText             = selectedText
+                eventList.selectedText             = selectedPlainText
             } else if (eventList.delegateWithSelectedText === model.id) {
                 eventList.delegateWithSelectedText = ""
                 eventList.selectedText             = ""
@@ -274,7 +274,7 @@ HRowLayout {
                 radius: theme.chat.message.radius
                 z: -100
                 color: eventDelegate.checked &&
-                       ! contentLabel.selectedText &&
+                       ! contentLabel.selectedPlainText &&
                        ! mousePointHandler.active &&
                        ! mouseShiftPointHandler.active ?
                        theme.chat.message.checkedBackground :