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>

test/components/views/beacon/RoomCallBanner-test.tsx

@@ -42,8 +42,8 @@ import RoomCallBanner from "../../../../src/components/views/beacon/RoomCallBann
 import { CallStore } from "../../../../src/stores/CallStore";
 import { WidgetMessagingStore } from "../../../../src/stores/widgets/WidgetMessagingStore";
 import { MatrixClientPeg } from "../../../../src/MatrixClientPeg";
-import { RoomViewStore } from "../../../../src/stores/RoomViewStore";
 import { ConnectionState } from "../../../../src/models/Call";
+import { SdkContextClass } from "../../../../src/contexts/SDKContext";
 
 describe("<RoomCallBanner />", () => {
     let client: Mocked<MatrixClient>;
@@ -132,7 +132,8 @@ describe("<RoomCallBanner />", () => {
         });
 
         it("doesn't show banner if the call is shown", async () => {
-            jest.spyOn(RoomViewStore.instance, 'isViewingCall').mockReturnValue(true);
+            jest.spyOn(SdkContextClass.instance.roomViewStore, "isViewingCall");
+            mocked(SdkContextClass.instance.roomViewStore.isViewingCall).mockReturnValue(true);
             await renderBanner();
             const banner = await screen.queryByText("Video call");
             expect(banner).toBeFalsy();