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/components/+preferences/add-helm-repo-dialog.tsx

@@ -13,7 +13,7 @@ import { systemName, isUrl, isPath } from "../input/input_validators";
 import { SubTitle } from "../layout/sub-title";
 import { Icon } from "../icon";
 import { Notifications } from "../notifications";
-import { HelmRepo, repoManager } from "../../../main/helm/helm-repo-manager";
+import { HelmRepo, HelmRepoManager } from "../../../main/helm/helm-repo-manager";
 
 interface Props extends Partial<DialogProps> {
   onAddRepo: Function
@@ -79,7 +79,7 @@ export class AddHelmRepoDialog extends React.Component<Props> {
 
   async addCustomRepo() {
     try {
-      await repoManager.addСustomRepo(this.helmRepo);
+      await HelmRepoManager.getInstance().addСustomRepo(this.helmRepo);
       Notifications.ok(<>Helm repository <b>{this.helmRepo.name}</b> has added</>);
       this.props.onAddRepo();
       this.close();