* hb_ot_color_has_svg
* hb_ot_color_glyph_svg_create_blob

* -Wshift-sign-overflow
* -Wmissing-prototypes

If a pointer type was passed to Null(), reinterpret_cast<> was
complaining about qualifiers being removed. Turns out I need the const on
the other side of "Type" to fix that.  Also remove unused const from
NullPool type.

Not sure if I like to keep it. For now, aim for correctness.

Common Regoin for Access Protection.  Like the NullPool, but writable.

Later to be expanded to a more general tool but for now it only supports CBDT, SVG and CBDT.

Fixes https://github.com/behdad/harfbuzz/issues/585

Fixes https://github.com/behdad/harfbuzz/issues/188
Fixes https://bugs.freedesktop.org/show_bug.cgi?id=93182

Avoids "deprecated" warnings.

Was introduced in glib 2.22.

Not really useful.

For two reasons:

1. User can always call hb_buffer_pre_allocate() themselves, and

2. Now we do a pre_alloc in add_utfX anyway, so the total number of
reallocs is limited to a small number (~3) anyway.  This just makes the
API cleaner.

Remove hb_ft_get_font_funcs() as it cannot be used by the user anyway.

Add hb_ft_font_set_funcs().  Which will make the font internally use
FreeType.  That is, no need for the font to have created using the
hb-ft API.  Just create using hb_face_create()/hb_font_create() and
then call this on the font (after having set font scale).  This
internally creates an FT_Face and attached to the font.