Improve type of selectors map

Improve the type of the `selectors` argument to `createStoreModule` to
link it to the type of the initial state returned by the `initialState`
argument. This enables TS to check/infer that the first argument to
these functions should be of the same type that `initialState` returns.

In the process it was necessary to remove the `ModuleConfig` type and
declare the type of `createStoreModule`'s `config` argument inline.
This works around a TypeScript limitation [1]:

```
@template State
@template {SelectorMap<State>} Selectors // Unexpected error
...
@typedef ModuleConfig
```

But this works:

``
@template State
@template {SelectorMap<State>} Selectors // OK
...
function createStoreModule(...) { ... }
```

[1] microsoft/TypeScript#43403

src/sidebar/store/create-store.js

@@ -23,23 +23,31 @@ import { createReducer, bindSelectors } from './util';
  */
 
 /**
- * Map of action name to reducer function.
+ * Map of action type to reducer function.
  *
  * @template State
- * @typedef {{ [action: string]: (s: State, action: any) => Partial<State> }} Reducers
+ * @typedef {{ [action: string]: (s: State, action: any) => Partial<State> }} ReducerMap
  */
 
 /**
- * Configuration for a store module.
+ * Map of selector name to selector function.
+ *
+ * @template State
+ * @typedef {{ [name: string]: (s: State, ...args: any[]) => any }} SelectorMap
+ */
+
+/**
+ * Type of a store module returned by `createStoreModule`.
  *
  * @template State
  * @template {object} Actions
  * @template {object} Selectors
  * @template {object} RootSelectors
- * @typedef ModuleConfig
+ * @typedef Module
  * @prop {string} namespace -
  *   The key under which this module's state will live in the store's root state
- * @prop {Reducers<State>} reducers -
+ * @prop {(...args: any[]) => State} initialState
+ * @prop {ReducerMap<State>} reducers -
  *   Map of action types to "reducer" functions that process an action and return
  *   the changes to the state
  * @prop {Actions} actionCreators
@@ -49,18 +57,6 @@ import { createReducer, bindSelectors } from './util';
  * @prop {RootSelectors} [rootSelectors]
  */
 
-/**
- * Type of a store module returned by `createStoreModule`.
- *
- * @template State
- * @template {object} Actions
- * @template {object} Selectors
- * @template {object} RootSelectors
- * @typedef {ModuleConfig<State, Actions, Selectors, RootSelectors> & {
- *   initialState: (...args: any[]) => State
- * }} Module
- */
-
 /**
  * Replace a type `T` with `Fallback` if `T` is `any`.
  *
@@ -191,15 +187,24 @@ export function createStore(modules, initArgs = [], middleware = []) {
   return store;
 }
 
+// The properties of the `config` argument to `createStoreModule` below are
+// declared inline due to https://github.com/microsoft/TypeScript/issues/43403.
+
 /**
  * Create a store module that can be passed to `createStore`.
  *
  * @template State
  * @template Actions
- * @template Selectors
+ * @template {SelectorMap<State>} Selectors
  * @template RootSelectors
  * @param {(...args: any[]) => State} initialState
- * @param {ModuleConfig<State,Actions,Selectors,RootSelectors>} config
+ * @param {object} config
+ *   @param {string} config.namespace -
+ *     The key under which this module's state will live in the store's root state
+ *   @param {ReducerMap<State>} config.reducers -
+ *   @param {Actions} config.actionCreators
+ *   @param {Selectors} config.selectors
+ *   @param {RootSelectors} [config.rootSelectors]
  * @return {Module<State,Actions,Selectors,RootSelectors>}
  */
 export function createStoreModule(initialState, config) {