Speed up search indexing.

The search indexing currently loads all PermissionGroups and
PermissionApps, which is slow.  To speed it up, we use the existing
list of platform permissions and only load what we need.

Change-Id: Id89fc290a1feb7add27969a07a09b912baab58fd
Fixes: 123666289
Test: Clear search index, it loads more quickly.