Ease HarfBuzz API change with feature detection

Skia has been using the not entirely public HarfBuzz subsetting API.
This API is changing for public release. In order to make the transition
from old to new build flags were added, which would require build
changes as HarfBuzz is updated downstream. Instead detect the existence
of the old or new API and use whichever is present automatically.

Change-Id: I0727f97ad7d394dfb24553076d4b383570cf0002
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437121
Reviewed-by: Garret Rieger <grieger@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
5 files changed