Fix sbix glyph extents

Fixes https://github.com/harfbuzz/harfbuzz/issues/1852

* The ‘height’ needs to be negated since the API returns “distance from
  top to bottom side”.
* Similarly, the ‘y_offset‘ needs to be added to the height to get the
  ‘y_bearing’, since sbix’s offset is “the point in the glyph relative
  to its lower-left corner which corresponds to the origin” while
  ‘y_bearing’ is the “top side of glyph from origin”.

With these changes the sbix glyph metrics return values similar to other
tables, as they were otherwise unusable.

As it is exposed with a different condition

Based on Konstantin Ritt work posted on mailing list

As searching number of hhea having fonts beats the number of OS/2
having ones in macOS 10.14.2

Fallback hhea's ascender/descender to OS2

Reinstates previous logic, even if it might be unnecessary.

I believe that was a try to use one approach as fallback to other.  But
felt wrong.  Just believe what's in OS/2 table to be correct.

Fixes https://github.com/harfbuzz/harfbuzz/pull/1432

This reverts commit 1c8654ea.

Let's see if 576065b4 has fixed it

This reverts commit b8e90ca1.

Works now.