Add Keys.Messages.seen_tooltips keybind

Toggle display of the focused message's seen counter tooltip,
which shows which user have this message as their last seen
and when did they send that information.
When this mode is active, you can move the focus
to other messages  and the tooltip will update itself.
If a message doesn't have a counter, it won't have a tooltip.

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

@@ -262,7 +262,15 @@ HRowLayout {
             }
 
             HToolTip {
-                visible: eventContent.hoveredLink === "#state-text"
+                readonly property bool keyboardShow:
+                    eventList.showFocusedSeenTooltips &&
+                    eventList.currentIndex === model.index &&
+                    model.read_by_count > 0
+
+                instant: keyboardShow
+                visible:
+                    eventContent.hoveredLink === "#state-text" || keyboardShow
+
                 label.textFormat: HLabel.StyledText
                 text: {
                     if (! visible) return ""

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

@@ -51,6 +51,13 @@ Rectangle {
             eventList.checkFromLastToHere(eventList.currentIndex)
     }
 
+    HShortcut {
+        sequences: window.settings.Keys.Messages.seen_tooltips
+        onActivated:
+            eventList.showFocusedSeenTooltips =
+            ! eventList.showFocusedSeenTooltips
+    }
+
     HShortcut {
         readonly property var events:
             eventList.selectedCount ?
@@ -237,6 +244,8 @@ Rectangle {
         property string delegateWithSelectedText: ""
         property string selectedText: ""
 
+        property bool showFocusedSeenTooltips: false
+
         property alias cursorShape: cursorShapeArea.cursorShape
 
         readonly property bool shouldLoadPastEvents: