Separate the header description and link.

We use the text under SettingsWithLargeHeader for both text (e.g.,
permission descriptions on PermissionAppsFragment) and links (e.g.,
"See all in Dashboard" in a filtered PermissionUsageFragment).  Split
them out into two separate entries (only one of which is visible at a
time) so we can apply separate styles.

Fixes: 130182794
Test: View the above screens.
Change-Id: Ifcc553a69da9a9de73b4102b162eeb09a83d8a60