Add tooltips for breadcrumbs

res/css/views/rooms/_RoomBreadcrumbs2.scss

@@ -51,3 +51,18 @@ limitations under the License.
         height: 32px;
     }
 }
+
+.mx_RoomBreadcrumbs2_Tooltip {
+    margin-left: -42px;
+    margin-top: -42px;
+
+    &.mx_Tooltip {
+        background-color: $tagpanel-bg-color;
+        color: $accent-fg-color;
+        border: 0;
+
+        .mx_Tooltip_chevron {
+            display: none;
+        }
+    }
+}

src/components/views/rooms/RoomBreadcrumbs2.tsx

@@ -26,6 +26,7 @@ import { UPDATE_EVENT } from "../../../stores/AsyncStore";
 import { CSSTransition } from "react-transition-group";
 import RoomListStore from "../../../stores/room-list/RoomListStore2";
 import { DefaultTagID } from "../../../stores/room-list/models";
+import AccessibleTooltipButton from "../elements/AccessibleTooltipButton";
 
 // TODO: Remove banner on launch: https://github.com/vector-im/riot-web/issues/14231
 // TODO: Rename on launch: https://github.com/vector-im/riot-web/issues/14231
@@ -98,11 +99,13 @@ export default class RoomBreadcrumbs2 extends React.PureComponent<IProps, IState
             const roomTags = RoomListStore.instance.getTagsForRoom(r);
             const roomTag = roomTags.includes(DefaultTagID.DM) ? DefaultTagID.DM : roomTags[0];
             return (
-                <AccessibleButton
+                <AccessibleTooltipButton
                     className="mx_RoomBreadcrumbs2_crumb"
                     key={r.roomId}
                     onClick={() => this.viewRoom(r, i)}
                     aria-label={_t("Room %(name)s", {name: r.name})}
+                    title={r.name}
+                    tooltipClassName={"mx_RoomBreadcrumbs2_Tooltip"}
                 >
                     <DecoratedRoomAvatar
                         room={r}
@@ -111,7 +114,7 @@ export default class RoomBreadcrumbs2 extends React.PureComponent<IProps, IState
                         displayBadge={true}
                         forceCount={true}
                     />
-                </AccessibleButton>
+                </AccessibleTooltipButton>
             );
         });