Move eventId getter to SimpleTile which is inherited by a few other tiles

See https://github.com/vector-im/hydrogen-web/pull/690#discussion_r817007275

src/domain/session/room/timeline/tiles/BaseMessageTile.js

@@ -49,10 +49,6 @@ export class BaseMessageTile extends SimpleTile {
         return `https://matrix.to/#/${encodeURIComponent(this.sender)}`;
     }
 
-    get eventId() {
-        return this._entry.id;
-    }
-
     get displayName() {
         return this._entry.displayName || this.sender;
     }

src/domain/session/room/timeline/tiles/SimpleTile.js

@@ -44,6 +44,10 @@ export class SimpleTile extends ViewModel {
         return this._entry.asEventKey();
     }
 
+    get eventId() {
+        return this._entry.id;
+    }
+
     get isPending() {
         return this._entry.isPending;
     }