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/main/__test__/kubeconfig-manager.test.ts

@@ -36,10 +36,6 @@ import * as path from "path";
 console = new Console(process.stdout, process.stderr); // fix mockFS
 
 describe("kubeconfig manager tests", () => {
-  beforeEach(() => {
-    jest.clearAllMocks();
-  });
-
   beforeEach(() => {
     const mockOpts = {
       "minikube-config.yml": JSON.stringify({
@@ -76,7 +72,7 @@ describe("kubeconfig manager tests", () => {
     const cluster = new Cluster({
       id: "foo",
       contextName: "minikube",
-      kubeConfigPath: "minikube-config.yml"
+      kubeConfigPath: "minikube-config.yml",
     });
     const contextHandler = new ContextHandler(cluster);
     const port = await getFreePort();
@@ -98,7 +94,7 @@ describe("kubeconfig manager tests", () => {
     const cluster = new Cluster({
       id: "foo",
       contextName: "minikube",
-      kubeConfigPath: "minikube-config.yml"
+      kubeConfigPath: "minikube-config.yml",
     });
     const contextHandler = new ContextHandler(cluster);
     const port = await getFreePort();