Not optimized to use sortedness yet.  Also start putting in place infra
to faster reject bad data.

A version of Chandas.ttf found on some Chrome bots has 660kb of GPOS,
mostly junk.  That is causing 48 million of set->add() calls in
collect_glyphs(), which is insane.

In the upcoming commits, I'll be speeding that up by optimizing
add_sorted_array(), while also reducing work by rejecting out-of-sort
arrays quickly and propagate the rejection.

Part of https://bugs.chromium.org/p/chromium/issues/detail?id=794896

Not hooked up to shaper yet.

Untested.

Still not hooked up from GPOS.

Not functional change (expected!).

This makes a lot of code safer.  We only try modifying the object in one
place, after making sure it's safe to do so.  So, do a const_cast<> in
that one place...

Simplifies hb_in_range() calls as the type can be inferred.
The rest is obsessiveness, I admit.

Avoids USHORT, SHORT, ULONG, LONG clashes with Windows API.

Should fix warnings generated when building with -Wunused-private-field.
Based on patch from Jonathan Kew.

More to come, for APPLY, CLOSURE, etc.

gdb was showing <anonymous enum> instead of useful stuff, so name
all our enums.

Where causing issues for people with MSVC.

Also change the Version type to avoid similar bugs in the future.

Reported by Grigori Goronzy.

I like this API *much* better.  Implementation still incomplete, but
horizontal works.

Design not final yet, and in fact I'm going to change it immediately,
but this is an standalone change for itself.

get_contour_point now takes glyph id before point_index.

get_kerning now takes a vector to fill-in.