Reimplement breadcrumbs for new room list

This all-new component handles breadcrumbs a bit more smoothly for the app by always listening to changes even if the component isn't present. This allows the breadcrumbs to remain up to date for when the user re-enables breadcrumbs.

The new behaviour is that we turn breadcrumbs on once the user has a room, and we don't turn it back off for them.

This also introduces a new animation which is more stable and not laggy, though instead of sliding the breadcrumbs pop. This might be undesirable - to be reviewed.

src/stores/AsyncStoreWithClient.ts

@@ -0,0 +1,53 @@
+/*
+Copyright 2020 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.
+*/
+
+import { MatrixClient } from "matrix-js-sdk/src/client";
+import { AsyncStore } from "./AsyncStore";
+import { ActionPayload } from "../dispatcher/payloads";
+
+
+export abstract class AsyncStoreWithClient<T extends Object> extends AsyncStore<T> {
+    protected matrixClient: MatrixClient;
+
+    protected abstract async onAction(payload: ActionPayload);
+
+    protected async onReady() {
+        // Default implementation is to do nothing.
+    }
+
+    protected async onNotReady() {
+        // Default implementation is to do nothing.
+    }
+
+    protected async onDispatch(payload: ActionPayload) {
+        await this.onAction(payload);
+
+        if (payload.action === 'MatrixActions.sync') {
+            // Filter out anything that isn't the first PREPARED sync.
+            if (!(payload.prevState === 'PREPARED' && payload.state !== 'PREPARED')) {
+                return;
+            }
+
+            this.matrixClient = payload.matrixClient;
+            await this.onReady();
+        } else if (payload.action === 'on_client_not_viable' || payload.action === 'on_logged_out') {
+            if (this.matrixClient) {
+                await this.onNotReady();
+                this.matrixClient = null;
+            }
+        }
+    }
+}