Export filegroups for XML and related code

See https://crrev.com/c/4405865 for context

Change-Id: I88976432325ed76be079e10ef224d5344854a51d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/669378
Commit-Queue: Christopher Cameron <ccameron@google.com>
Reviewed-by: Christopher Cameron <ccameron@google.com>
Auto-Submit: Kevin Lubick <kjlubick@google.com>
6 files changed