Fixes https://github.com/harfbuzz/harfbuzz/issues/1308

Was good idea, but with C++ types with constructor/destructor, was getting in
the way as compiler was destructing those items where it was not desired.
Since C++ does not allow zero-sized arrays, just remove it...

Fixes https://github.com/harfbuzz/harfbuzz/issues/1491

Not needed.  We get it in our config.h automatically thanks to
AC_USE_SYSTEM_EXTENSIONS.  Let's see whose build it breaks...
If we end up putting it back, we should add other things from
that macro and remove the macro.

Since it was pages and pages...

That's better use of that value than requiring extra macro HB_NO_ATEXIT

Fixes #1235.

Cygwin is a Posix platform to the extent possible.  It should use the
Posix API except in special circumstances.

Disable copy/assign on them, as they shouldn't.

Make constructor / destructor call init_shallow/fini_shallow,
and make those idempotent.  So, these three can be constructed
on stack now and no init/fini call is needed.  As such,
hb_auto_t<> is not needed anymore.  I'll remove that separately.

Older C++ doesn't allow struct-with-constructor in union.

Newer compilers / language allows structs with constructor in union.
So, this was not actually testing anything.  Indeed, the recent
change in DISALLOW_COPY *is* making some of our types non-POD.
That broke some bots.

Just remove this since it wasn't doing much, and I'd rather have
DISALLOW_COPY.

Finally!  Catches hard-to-find errors like this:

-    const SortedArrayOf<SVGDocumentIndexEntry> docs = this+svgDocEntries;
+    const SortedArrayOf<SVGDocumentIndexEntry> &docs = this+svgDocEntries;

We implement this for our array types.  This, in turn, trickles down
into all types that embed the arrays.  So, as long as we define all
open-ended structs in terms of Array types (all can be done using
UnsizedArrayOf), this achieves the goal of making uncopyable all
structs that are variable-sized.  Yay!

Fixes https://github.com/harfbuzz/harfbuzz/issues/1299

Removes anomaly I was seeing in cpal table trying to use implicit Null(NameID).

Fixes https://github.com/harfbuzz/harfbuzz/issues/1247

Enabled if script tag 'Qaag' is passed to HarfBuzz.  Disables mark
advance-zeroing and fallback mark-positioning.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1162

We never tested compiling without it.  Just kill it.  We always build
our own shaper.