Fixing Singleton typing to correctly return child class (#1914)

- Add distinction between `getInstance` and `getInstanceOrCreate` since
  it is not always possible to create an instance (since you might not
  know the correct arguments)

- Remove all the `export const *Store = *Store.getInstance<*Store>();`
  calls as it defeats the purpose of `Singleton`. Plus with the typing
  changes the appropriate `*Store.getInstance()` is "short enough".

- Special case the two extension export facades to not need to use
  `getInstanceOrCreate`. Plus since they are just facades it is always
  possible to create them.

- Move some other types to be also `Singleton`'s: ExtensionLoader,
  ExtensionDiscovery, ThemeStore, LocalizationStore, ...

- Fixed dev-run always using the same port with electron inspect

- Update Store documentation with new recommendations about creating
  instances of singletons

- Fix all unit tests to create their dependent singletons

Signed-off-by: Sebastian Malton <sebastian@malton.name>

src/renderer/utils/__tests__/storageHelper.test.ts

@@ -1,8 +1,17 @@
 import { reaction } from "mobx";
 import { StorageAdapter, StorageHelper } from "../storageHelper";
 import { delay } from "../../../common/utils/delay";
+import { ClusterStore } from "../../../common/cluster-store";
 
 describe("renderer/utils/StorageHelper", () => {
+  beforeEach(() => {
+    ClusterStore.getInstanceOrCreate();
+  });
+
+  afterEach(() => {
+    ClusterStore.resetInstance();
+  });
+
   describe("window.localStorage might be used as StorageAdapter", () => {
     type StorageModel = string;