HarfBuzz 2.x has native support for AAT fonts which is, according to Chrome
developers, sgnificantly faster that HarfBuzz Core Text integration.

Change-Id: I4d5e861a1958402a6e3ccb720b10f40828c3db6a
Reviewed-on: https://gerrit.libreoffice.org/68919
Tested-by: Jenkins
Reviewed-by: Khaled Hosny <khaledhosny@eglug.org>