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/components/structures/MatrixChat.tsx

@@ -137,6 +137,7 @@ import { TimelineRenderingType } from "../../contexts/RoomContext";
 import { UseCaseSelection } from '../views/elements/UseCaseSelection';
 import { ValidatedServerConfig } from '../../utils/ValidatedServerConfig';
 import { isLocalRoom } from '../../utils/localRoom/isLocalRoom';
+import { SdkContextClass, SDKContext } from '../../contexts/SDKContext';
 import { viewUserDeviceSettings } from '../../actions/handlers/viewUserDeviceSettings';
 
 // legacy export
@@ -238,9 +239,12 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
     private readonly dispatcherRef: string;
     private readonly themeWatcher: ThemeWatcher;
     private readonly fontWatcher: FontWatcher;
+    private readonly stores: SdkContextClass;
 
     constructor(props: IProps) {
         super(props);
+        this.stores = SdkContextClass.instance;
+        this.stores.constructEagerStores();
 
         this.state = {
             view: Views.LOADING,
@@ -762,6 +766,7 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
                 Modal.createDialog(DialPadModal, {}, "mx_Dialog_dialPadWrapper");
                 break;
             case Action.OnLoggedIn:
+                this.stores.client = MatrixClientPeg.get();
                 if (
                     // Skip this handling for token login as that always calls onLoggedIn itself
                     !this.tokenLogin &&
@@ -2087,7 +2092,9 @@ export default class MatrixChat extends React.PureComponent<IProps, IState> {
         }
 
         return <ErrorBoundary>
-            { view }
+            <SDKContext.Provider value={this.stores}>
+                { view }
+            </SDKContext.Provider>
         </ErrorBoundary>;
     }
 }