Move api-derive to correct location (#4343)

* Move api-derive to correct location

* Adjust (linting ok)

* No composite

* ApiDerive split

* Adjust

* Still WIP, getting closer

* It lints

* derive build issues sorted

* It builds :)

* Add system_health to mock

* api-augment usage

* Cleanups

* Adjust paths

* linting

* Some <'s

* Revert <>'s

* linting

* ordering

* Augmentation tweaks

* yarn.lock

* export

packages/api-derive/src/staking/overview.ts

@@ -0,0 +1,26 @@
+// Copyright 2017-2021 @polkadot/api-derive authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+import type { Observable } from 'rxjs';
+import type { DeriveApi, DeriveStakingOverview } from '../types';
+
+import { combineLatest, map } from 'rxjs';
+
+import { memo } from '../util';
+
+/**
+ * @description Retrieve the staking overview, including elected and points earned
+ */
+export function overview (instanceId: string, api: DeriveApi): () => Observable<DeriveStakingOverview> {
+  return memo(instanceId, (): Observable<DeriveStakingOverview> =>
+    combineLatest([
+      api.derive.session.indexes(),
+      api.derive.staking.validators()
+    ]).pipe(
+      map(([indexes, { nextElected, validators }]): DeriveStakingOverview => ({
+        ...indexes,
+        nextElected,
+        validators
+      }))
+    ));
+}