CrOS Settings: Crostini shared files settings page

Added new 'Manage files & folders' section to crostini settings page.
This shows which folders from Chrome OS (e.g. Downloads/foo) are shared
with crostini, and allows the unshare them.

Bug: 878324
Change-Id: I7d8090d84024c7ca834ef614da14297eb0a2ed69
Reviewed-on: https://chromium-review.googlesource.com/c/1270380
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598578}
21 files changed