Improve URL Previews

only show 2 by default with expand/collapse mechanism
show all hashes again, but dedup requests
clean up hide mechanism, instead of one `x` per preview have one per group

res/css/_components.scss

@@ -201,6 +201,7 @@
 @import "./views/rooms/_GroupLayout.scss";
 @import "./views/rooms/_IRCLayout.scss";
 @import "./views/rooms/_JumpToBottomButton.scss";
+@import "./views/rooms/_LinkPreviewGroup.scss";
 @import "./views/rooms/_LinkPreviewWidget.scss";
 @import "./views/rooms/_MemberInfo.scss";
 @import "./views/rooms/_MemberList.scss";

res/css/views/rooms/_LinkPreviewGroup.scss

@@ -0,0 +1,38 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+.mx_LinkPreviewGroup {
+    .mx_LinkPreviewGroup_hide {
+        cursor: pointer;
+        width: 18px;
+        height: 18px;
+
+        img {
+            flex: 0 0 40px;
+            visibility: hidden;
+        }
+    }
+
+    &:hover .mx_LinkPreviewGroup_hide img,
+    .mx_LinkPreviewGroup_hide.focus-visible:focus img {
+        visibility: visible;
+    }
+
+    > .mx_AccessibleButton {
+        color: $accent-color;
+        text-align: center;
+    }
+}

res/css/views/rooms/_LinkPreviewWidget.scss

@@ -51,22 +51,6 @@ limitations under the License.
     word-wrap: break-word;
 }
 
-.mx_LinkPreviewWidget_cancel {
-    cursor: pointer;
-    width: 18px;
-    height: 18px;
-
-    img {
-        flex: 0 0 40px;
-        visibility: hidden;
-    }
-}
-
-.mx_LinkPreviewWidget:hover .mx_LinkPreviewWidget_cancel img,
-.mx_LinkPreviewWidget_cancel.focus-visible:focus img {
-    visibility: visible;
-}
-
 .mx_MatrixChat_useCompactLayout {
     .mx_LinkPreviewWidget {
         margin-top: 6px;