Store refactor: use non-global stores in components (#9293)

* Add Stores and StoresContext and use it in MatrixChat and RoomView

Added a new kind of class:
- Add God object `Stores` which will hold refs to all known stores and the `MatrixClient`. This object is NOT a singleton.
- Add `StoresContext` to hold onto a ref of `Stores` for use inside components.

`StoresContext` is created via:
- Create `Stores` in `MatrixChat`, assigning the `MatrixClient` when we have one set. Currently sets the RVS to `RoomViewStore.instance`.
- Wrap `MatrixChat`s `render()` function in a `StoresContext.Provider` so it can be used anywhere.

`StoresContext` is currently only used in `RoomView` via the following changes:
- Remove the HOC, which redundantly set `mxClient` as a prop. We don't need this as `RoomView` was using the client from `this.context`.
- Change the type of context accepted from `MatrixClientContext` to `StoresContext`.
- Modify alllll the places where `this.context` is used to interact with the client and suffix `.client`.
- Modify places where we use `RoomViewStore.instance` and replace them with `this.context.roomViewStore`.

This makes `RoomView` use a non-global instance of RVS.

* Linting

* SDKContext and make client an optional constructor arg

* Move SDKContext to /src/contexts

* Inject all RVS deps

* Linting

* Remove reset calls; deep copy the INITIAL_STATE to avoid test pollution

* DI singletons used in RoomView; DI them in RoomView-test too

* Initial RoomViewStore.instance after all files are imported to avoid cyclical deps

* Lazily init stores to allow for circular dependencies

Rather than stores accepting a list of other stores in their constructors,
which doesn't work when A needs B and B needs A, make new-style stores simply
accept Stores. When a store needs another store, they access it via `Stores`
which then lazily constructs that store if it needs it. This breaks the
circular dependency at constructor time, without needing to introduce
wiring diagrams or any complex DI framework.

* Delete RoomViewStore.instance

Replaced with Stores.instance.roomViewStore

* Linting

* Move OverridableStores to test/TestStores

* Rejig how eager stores get made; don't automatically do it else tests break

* Linting

* Linting and review comments

* Fix new code to use Stores.instance

* s/Stores/SdkContextClass/g

* Update docs

* Remove unused imports

* Update src/stores/RoomViewStore.tsx

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

* Remove empty c'tor to make sonar happy

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

src/stores/room-list/RoomListStore.ts

@@ -27,7 +27,6 @@ import { ActionPayload } from "../../dispatcher/payloads";
 import defaultDispatcher from "../../dispatcher/dispatcher";
 import { readReceiptChangeIsFor } from "../../utils/read-receipts";
 import { FILTER_CHANGED, IFilterCondition } from "./filters/IFilterCondition";
-import { RoomViewStore } from "../RoomViewStore";
 import { Algorithm, LIST_UPDATED_EVENT } from "./algorithms/Algorithm";
 import { EffectiveMembership, getEffectiveMembership } from "../../utils/membership";
 import RoomListLayoutStore from "./RoomListLayoutStore";
@@ -40,6 +39,7 @@ import { IRoomTimelineActionPayload } from "../../actions/MatrixActionCreators";
 import { RoomListStore as Interface, RoomListStoreEvent } from "./Interface";
 import { SlidingRoomListStoreClass } from "./SlidingRoomListStore";
 import { UPDATE_EVENT } from "../AsyncStore";
+import { SdkContextClass } from "../../contexts/SDKContext";
 
 interface IState {
     // state is tracked in underlying classes
@@ -105,7 +105,7 @@ export class RoomListStoreClass extends AsyncStoreWithClient<IState> implements
             this.readyStore.useUnitTestClient(forcedClient);
         }
 
-        RoomViewStore.instance.addListener(UPDATE_EVENT, () => this.handleRVSUpdate({}));
+        SdkContextClass.instance.roomViewStore.addListener(UPDATE_EVENT, () => this.handleRVSUpdate({}));
         this.algorithm.on(LIST_UPDATED_EVENT, this.onAlgorithmListUpdated);
         this.algorithm.on(FILTER_CHANGED, this.onAlgorithmFilterUpdated);
         this.setupWatchers();
@@ -128,7 +128,7 @@ export class RoomListStoreClass extends AsyncStoreWithClient<IState> implements
     private handleRVSUpdate({ trigger = true }) {
         if (!this.matrixClient) return; // We assume there won't be RVS updates without a client
 
-        const activeRoomId = RoomViewStore.instance.getRoomId();
+        const activeRoomId = SdkContextClass.instance.roomViewStore.getRoomId();
         if (!activeRoomId && this.algorithm.stickyRoom) {
             this.algorithm.setStickyRoom(null);
         } else if (activeRoomId) {