ref: replace hardcoded types with StoreApi type (#1459)

Add binding of createStoreImpl methods types to StoreApi without hardcoding.
Makes it easier to read and reason about where the type comes from and belongs to.
Removing arrow function types reduces number of arrows, and makes it easier to read.

src/vanilla.ts

@@ -60,7 +60,7 @@ const createStoreImpl: CreateStoreImpl = (createState) => {
   let state: TState
   const listeners: Set<Listener> = new Set()
 
-  const setState: SetStateInternal<TState> = (partial, replace) => {
+  const setState: StoreApi<TState>['setState'] = (partial, replace) => {
     // TODO: Remove type assertion once https://github.com/microsoft/TypeScript/issues/37663 is resolved
     // https://github.com/microsoft/TypeScript/issues/37663#issuecomment-759728342
     const nextState =
@@ -77,15 +77,15 @@ const createStoreImpl: CreateStoreImpl = (createState) => {
     }
   }
 
-  const getState: () => TState = () => state
+  const getState: StoreApi<TState>['getState'] = () => state
 
-  const subscribe: (listener: Listener) => () => void = (listener) => {
+  const subscribe: StoreApi<TState>['subscribe'] = (listener) => {
     listeners.add(listener)
     // Unsubscribe
     return () => listeners.delete(listener)
   }
 
-  const destroy: () => void = () => listeners.clear()
+  const destroy: StoreApi<TState>['destroy'] = () => listeners.clear()
   const api = { setState, getState, subscribe, destroy }
   state = createState(setState, getState, api)
   return api as any