[gapi] Add typings for token session_state (#36121)

* Add typings for token session_state

* Add getToken() to gapi.client

types/gapi/index.d.ts

@@ -20,12 +20,19 @@ interface GoogleApiOAuth2TokenObject {
      * The duration, in seconds, the token is valid for. Only present in successful responses
      */
     expires_in: string;
+    session_state: GoogleApiOAuth2TokenSessionState;
     /**
      * The Google API scopes related to this token
      */
     state: string;
 }
 
+interface GoogleApiOAuth2TokenSessionState {
+    extraQueryParams: {
+        authuser: string,
+    };
+}
+
 /**
  * Fix for #8215
  * https://github.com/DefinitelyTyped/DefinitelyTyped/issues/8215
@@ -230,6 +237,11 @@ declare namespace gapi.client {
      * @param apiKey The API key to set
      */
     export function setApiKey(apiKey: string): void;
+    /**
+     * Retrieves the OAuth 2.0 token for the application.
+     * @return The OAuth 2.0 token.
+     */
+    export function getToken(): GoogleApiOAuth2TokenObject;
     /**
      * Sets the authentication token to use in requests.
      * @param token The token to set.