Fix permissions and multi-select for SearchResults

Before, you were not able to select multiple items when searching
for files.  You also wouldn't be able to edit those items even
if you had manage_files permissions.  This fixes both of
those bugs.

fixes CNVS-15800
fixes CNVS-15834

test plan:
- Enable Better File Browsing feature flag
- Go to any course's Files section
- Search for an existing file
- Click on the search result(s) in the main file pane
- A toolbar should appear above allowing you to
  view and download the file(s), as well as other
  editing abilities if you have manage_files permissions.
  Also, if you have manage_files permissions, a PublishCloud
  button should appear on each search result item,
  as well as additional options in the ItemCog to edit, move,
  etc that file (more than just the Download link).

Change-Id: Ie818fd1cf4cd7dcaa0520260babf5a540ca816e4
Reviewed-on: https://gerrit.instructure.com/41801
Reviewed-by: Ryan Shaw <ryan@instructure.com>
Product-Review: Ryan Shaw <ryan@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Anna Koalenz <akoalenz@instructure.com>