Allow students to access files in hidden folders

This commit fixes a bug where a teacher would
restrict a folder so that it is "Hidden, available
with link" and none of the published/available
files within the folder could be accessed.

Fixes CNVS-17579

Test Plan:
* Enable "Better File Browsing" feature flag
* Go to a course's Files page as admin/teacher
* Select a folder in the file pane, then click
  "Restrict Access"

Part 1: Verbiage Changes based on Selection
* On the modal that appears, select "Restricted Access"
* The first radio button that appears below should read
  "Hidden, files inside will be available with links." -
  select this radio button and click "Update"
* Select multiple folders and click "Restrict Access"
* Select "Restrict Access" and the message for the first
  radio button should be the same as above
* Close the dialog
* Select multiple files and folders
* Click "Restrict Access" -> "Restricted Access"
* The radio option should read "Files and folder contents
  only available to students with link. Not visible in
  student files."
* Close the dialog
* Select a file or multiple files (not folders)
* Click "Restrict Access" -> "Restricted Access"
* The radio option should read "Only available to students
  with link. Not visible in student files."
* Close the dialog

Part 2, Continued from Above: Files Available to Access
* Go to the first folder that you restricted access to
* Select a file in the folder and make sure it's published
  or otherwise available to students
* Click "View"
* Copy the URI in your address bar
* Open an incognito browser and log into canvas as a student
  who is enrolled in the same course as the user you used
  before
* Paste the URI you copied into the address bar and go
* The browser should go to the course's Files page
  with a preview window opened of the file within
  the restricted folder
* The URI in the address bar should be the course's
  root folder (e.g. /courses/1/files?preview=123)

Change-Id: I7d8da0457528b43454fce2927f440b89c67c5532
Reviewed-on: https://gerrit.instructure.com/46195
Reviewed-by: Clay Diffrient <cdiffrient@instructure.com>
Product-Review: Cosme Salazar <cosme@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jahnavi Yetukuri <jyetukuri@instructure.com>