TV: Use Storage strings instead of FG/Always

So that the permissions on TV show as:

 * Allow management of all files (if requesting MANAGE)
 * Allow accses to media only (if requesting READ)
 * Don't allow

Instead of:

 * Allow all the time
 * While using the app
 * Don't allow

Which has been confusing people.

Bug: 215405004
Test: Inspection - open the Files app in PermissionController and look
Change-Id: I0708a2c51d13c24c8c99eda6b8a0bd9988444810
(cherry picked from commit 64de4969)