packages/core: move LoginPage to layouts and remove it as a hardcoded route in the app (#1020)

packages/app/src/App.tsx

@@ -14,9 +14,14 @@
  * limitations under the License.
  */
 
-import { createApp, AlertDisplay, OAuthRequestDialog } from '@backstage/core';
+import {
+  createApp,
+  AlertDisplay,
+  OAuthRequestDialog,
+  LoginPage,
+} from '@backstage/core';
 import React, { FC } from 'react';
-import { BrowserRouter as Router } from 'react-router-dom';
+import { BrowserRouter as Router, Route } from 'react-router-dom';
 import Root from './components/Root';
 import * as plugins from './plugins';
 import apis from './apis';
@@ -35,6 +40,7 @@ const App: FC<{}> = () => (
     <OAuthRequestDialog />
     <Router>
       <Root>
+        <Route key="login" path="/login" component={LoginPage} exact />,
         <AppComponent />
       </Root>
     </Router>