Resolve import cycle to improve tool compatibility

This change resolves the cyclical import dependency
`store-devtools/src/{provide-store-devtools <-> instrument}.ts` by
moving `createStateObservable` to `provide-store-devtools.ts`, its only
user.

modules/store-devtools/src/instrument.ts

@@ -1,15 +1,7 @@
 import { ModuleWithProviders, NgModule } from '@angular/core';
-import { StateObservable } from '@ngrx/store';
 import { StoreDevtoolsOptions } from './config';
-import { StoreDevtools } from './devtools';
 import { provideStoreDevtools } from './provide-store-devtools';
 
-export function createStateObservable(
-  devtools: StoreDevtools
-): StateObservable {
-  return devtools.state;
-}
-
 @NgModule({})
 export class StoreDevtoolsModule {
   static instrument(

modules/store-devtools/src/provide-store-devtools.ts

@@ -19,7 +19,6 @@ import {
   StoreDevtoolsOptions,
 } from './config';
 import { ReducerManagerDispatcher, StateObservable } from '@ngrx/store';
-import { createStateObservable } from './instrument';
 import { StoreDevtools } from './devtools';
 
 export const IS_EXTENSION_OR_MONITOR_PRESENT = new InjectionToken<boolean>(
@@ -46,6 +45,12 @@ export function createReduxDevtoolsExtension() {
   }
 }
 
+export function createStateObservable(
+  devtools: StoreDevtools
+): StateObservable {
+  return devtools.state;
+}
+
 /**
  * Provides developer tools and instrumentation for `Store`.
  *