Fixes https://github.com/harfbuzz/harfbuzz/issues/1146

See a85641446c30247c4e948263f0f8c1147ed4efb9

Add pointer cast operator and plus operator.

From bungeman.

Fixes https://github.com/harfbuzz/harfbuzz/pull/1314

Ugly, but...
Fixes https://github.com/harfbuzz/harfbuzz/issues/1227

Fixes https://github.com/harfbuzz/harfbuzz/issues/1145

There might be a better way to do this, but I couldn't find...

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

New API:
HB_UNICODE_MAX

And use.

To be moved to hb-face.h later.

To be moved to hb-face later.

Don't use accelerator (almost).  Hooks up Format13 as well.

OpenType cmap table can use gid=0 to mean "not covered" to produce
more optimized cmap subtables.  Return false from get_nominal_glyph()
for those.  hb-ft already does this.

When collecting all codepoints in the cmap avoid using large amount of memory for fonts that declare coverage over all 32 bit integers.