We're experiencing users in Chrome that require larger decode sizes for their woff2 fonts. I suggest to increase this limit. Compare https://crbug.com/40233227
overlapSimpleBitmap is a new field in the transformed glyf table (https://www.w3.org/TR/WOFF2/#glyf_table_format). It allows the overlap simple flag set on glyphs in the original font to be saved into the woff2 encoding.
This is a first step to make WOFF2 a shared library. Public headers are moved
in their own directory to make the public API clearer. This is similar to
the c/include/brotli/ directory in Brotli. "using" commands are also removed
from the public headers, so that callers won't have unexpected side effect
when including the files.