Set user_return_to in GET /maker/google_oauth_confirm_login

[maddiedierker]

This bug came up while investigating a different ticket -- STAR-1496 (using Google OAuth from the Maker App fails for users with unmigrated accounts).

Local repro steps (these don't repro on production because the bug hadn't been released yet):

1. Click “log in with google” in the Maker App
2. Click “confirm” from the browser tab that opens after step 1
3. Go through the Google OAuth process

Expected: the browser redirects to /maker/display_google_oauth_code with the “magic code” to copy-paste back into the Maker App
Actual: the browser redirects to /home

This was happening because in browser/#76, we changed the "Login with Google" route in the Maker App:

• old route: GET /users/sign_in?user_return_to=/maker/display_google_oauth_code
• new route: GET /maker/google_oauth_confirm_login?user_return_to=/maker/display_google_oauth_code

This change was intentional, but broke the user_return_to feature because the old route set session[:user_return_to], but the new route didn't. Now, session[:user_return_to] will be set in the new route.

Testing story

Added an integration test for this scenario.

[epeach]

Good catch on this before release!