Sorry for the noise, downstream custom builders.  Please adjust.

Found and fixed a couple bugs.

Found a couple multithreading issues.  Marked them with "XXX-MT-bug".

Fixes #791.

Fixes https://github.com/behdad/harfbuzz/issues/615

We'll see which bots I broke.

* Fix missing xscale in rtl graphite unpacking

* Oops didn't need to mess with yscale

It is unused after previous commit, hb_graphite2_font_get_gr_font()
makes no sense now so deprecating it.

Shape using design units and scale the output.

See https://bugs.documentfoundation.org/show_bug.cgi?id=103403#c7

Shape-plan caching is not implemented.

Fixes https://github.com/behdad/harfbuzz/issues/103

Based on patch from Martin Hosken, with review from Jonathan and I.

Patch from Martin Hosken.  I expect this to fix the following bugs:

https://bugs.freedesktop.org/show_bug.cgi?id=75076
https://bugzilla.gnome.org/show_bug.cgi?id=723582
https://bugzilla.redhat.com/show_bug.cgi?id=998812

https://bugs.webkit.org/show_bug.cgi?id=113796

Part of patch from Martin Hosken.  I believe he knows what he's doing
:).

Based on patch from Martin Hosken.  I believe it returns NULL if the
font doesn't have graphite tables, but have not tested.

Part of patch from Martin Hosken.