This adds to the autotools build system so that the (experimental)
DirectWrite support for HarfBuzz is built (and dist'ed).

This adds a set of NMake Makefiles that can be used to build HarfBuzz, from
the standard basic build building the minimal HarfBuzz DLL (consisting
of OpenType, fallback and Uniscribe support only), to a full fledged build
consisting of GLib and FreeType support, as well as building the utilities,
the test programs in src/ and test/api, and HarfBuzz-ICU and
HarfBuzz-GObject, and up to building the introspection files.  This means a
flexible build mechanism is supported here, so anything that is supported
for a Windows build (code-wise), should all be supported by this build
system.

As in an earlier commit, the source listings are shared with the autotools
builds with the various Makefile.sources in src/, src/hb-ucdn and util/, and
this set of NMake Makefiles will transform these lists into the form they
want.

In the current form, all the test programs in test/api pass, and this has
been checked successfully with 'make -j8 distcheck'.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=64501

This is a tool that lists all fonts that can render a given string.
It uses hb_shape() to do so, and as such is aware of HarfBuzz's
normalizer.

When I originally wrote hb-ft, FreeType objects did not support reference
counting.  As such, hb_ft_face_create() and hb_ft_font_create() had a
"destroy" callback and client was responsible for making sure FT_Face is
kept around as long as the hb-font/face are alive.

However, since this was not clearly documented, some clienets didn't
correctly did that.  In particular, some clients assumed that it's safe
to destroy FT_Face and then hb_face_t.  This, indeed, used to work, until
45fd9424, which make face destroy access
font tables.

Now, I fixed that issue in 395b3590 since
the access was not needed, but the problem remains that not all clients
handle this correctly.  See:

  https://bugs.freedesktop.org/show_bug.cgi?id=86300

Fortunately, FT_Reference_Face() was added to FreeType in 2010, and so we
can use it now.  Originally I wanted to change hb_ft_face_create() and
hb_ft_font_create() to reference the face if destroy==NULL was passed in.
That would improve pretty much all clients, with little undesired effects.
Except that FreeType itself, when compiled with HarfBuzz support, calls
hb_ft_font_create() with destroy==NULL and saves the resulting hb-font on
the ft-face (why does it not free it immediately?).  Making hb-face
reference ft-face causes a cycling reference there.  At least, that's my
current understanding.

At any rate, a cleaner approach, even if it means all clients will need a
change, is to introduce brand new API.  Which this commit does.

Some comments added to hb-ft.h, hoping to make future clients make better
choices.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=75299

We require FreeType >= 2.8.3.  This symbol was introduced earlier
than that.

Previous commit was not compiling with clang.

As in building for Android / iPhone.  Only set it if
struct{char} alignment is not 1.

NOT tested on an actual Arm architecture.  Guess we'll know
when this makes it to people's build bots.

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=75384

On iOS CoreText and CoreGraphics are stand-alone frameworks