Allow "replying" to an event with a file

Send a pseudo-reply consisting of two messages: a `m.text` which is just
a reply with an empty body, then the file event itself.

This is a workaround to the restriction imposed by the Matrix API,
which prevents us from simply attaching a reply to a media event:
https://matrix.org/docs/spec/client_server/latest#rich-replies

src/gui/Pages/Chat/Chat.qml

@@ -28,6 +28,14 @@ Item {
     readonly property bool composerHasFocus:
         Boolean(loader.item && loader.item.composer.hasFocus)
 
+    function clearReplyTo() {
+        if (! replyToEventId) return
+
+        replyToEventId     = ""
+        replyToUserId      = ""
+        replyToDisplayName = ""
+    }
+
 
     onFocusChanged: if (focus && loader.item) loader.item.composer.takeFocus()
     onReadyChanged: longLoading = false

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

@@ -98,14 +98,6 @@ HTextArea {
         py.callClientCoro(userId, "room_typing", [chat.roomId, typing])
     }
 
-    function clearReplyTo() {
-        if (! chat.replyToEventId) return
-
-        chat.replyToEventId     = ""
-        chat.replyToUserId      = ""
-        chat.replyToDisplayName = ""
-    }
-
     function addNewLine() {
         let indents = 0
         const parts = lineText.split(indent)
@@ -171,7 +163,9 @@ HTextArea {
             userId: chat.userId,
             roomId: chat.roomId,
             roomName: chat.roomInfo.display_name,
+            replyToEventId: chat.replyToEventId,
         },
+        popup => popup.replied.connect(chat.clearReplyTo),
     )
 
     Keys.onEscapePressed:

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

@@ -28,7 +28,9 @@ HButton {
                 roomId: chat.roomId,
                 roomName: chat.roomInfo.display_name,
                 filePath: Clipboard.text.trim(),
+                replyToEventId: chat.replyToEventId,
             },
+            popup => popup.replied.connect(chat.clearReplyTo),
         )
     }
 
@@ -36,6 +38,8 @@ HButton {
         id: sendFilePicker
         userId: chat.userId
         roomId: chat.roomId
+        replyToEventId: chat.replyToEventId
+        onReplied: chat.clearReplyTo()
 
         HShortcut {
             sequences: window.settings.keys.sendFile