Remove assumption about Core Text working in 96 DPI

Not have used it personally for a long time, lets remove it

Core Text seems to apply them to Latin text, but Uniscribe doesn’t.

See https://github.com/harfbuzz/harfbuzz/pull/1908#issuecomment-521819343

Fixes https://github.com/harfbuzz/harfbuzz/issues/1907

Needed for other works

Use hb_font_t coords directly

Set caret_count to zero as that is what we want to happen inside lcar when
there is no result.

I *think* it should fix https://github.com/harfbuzz/harfbuzz/issues/1901

Ie. if on a system, alignof(void*) < sizeof(void*)...

To satisfy -valgrind and -tsan bots, very ugly

vcpkg apparently doesn't like to work the same way used to anymore, lets disable it

https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6opbd.html

It has a different semantic, maybe we should just do a zero memset,
letting Behdad to decide.