Update maxp to use the correct num glyphs.

Part of https://github.com/harfbuzz/harfbuzz/issues/1553

Show up with gcc -O0.

There's a few more but those are functions that need to be filled in.

Maybe this is a lost battle...

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

Such a headache that Windows defines UINT8, ...; Just prefix it.

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.