hb_font_get_glyph_extents now works for color bitmap fonts.
Currently only font having index format 1 and image format 17
is supported.

Ouch!

Remove inexistent file ttx file from test/api/Makefile.am

[ci] Enable hb-freetype on Windows build tests

Make Uniscribe optional on nmake win32 builds

Most of harfbuzz clients don't need Uniscribe and DirectWrite support at all
as harfbuzz is a replacement for Uniscribe so Chromium and Firefox are using
harfbuzz without them on Windows.

This removal also helps win32 nmake clients to have reduced binary size and
libs count.

Fixes https://github.com/behdad/harfbuzz/issues/342

[ci] Whitelist more symbols and unbreak mac CI

Thanks to @khaledhosny, actually this is his work :)

Fixes https://github.com/behdad/harfbuzz/issues/336

Supercedes https://github.com/behdad/harfbuzz/pull/326
Fixes https://github.com/behdad/harfbuzz/pull/331

With this, I believe MATH table API is not ready to be merged.