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/migrations/hotbar-store/5.0.0-alpha.0.ts

@@ -1,6 +1,6 @@
 // Cleans up a store that had the state related data stored
 import { Hotbar } from "../../common/hotbar-store";
-import { clusterStore } from "../../common/cluster-store";
+import { ClusterStore } from "../../common/cluster-store";
 import { migration } from "../migration-wrapper";
 
 export default migration({
@@ -8,7 +8,7 @@ export default migration({
   run(store) {
     const hotbars: Hotbar[] = [];
 
-    clusterStore.enabledClustersList.forEach((cluster: any) => {
+    ClusterStore.getInstance().enabledClustersList.forEach((cluster: any) => {
       const name = cluster.workspace || "default";
       let hotbar = hotbars.find((h) => h.name === name);