fix: new_from_descriptor lose font variations, such as font-weight

[kaiwk]

If we create CTFont from font descriptor, we will lose font variations, and use new_from_name instead will fix it.

CTFontDescriptor is essentially a dictionary of font attributes.

[jrmuizel]

Can you add a test?

[kaiwk]

@jrmuizel I have to add CTFontManagerCreateFontDescriptorsFromData, because it happens when loading font from 'otc/ttc'.

I encountered the issue when using font-kit, font-kit manually unpack 'otc/ttc', I suppose it won't make any difference here.

[kaiwk]

The test failed on xcode 7.3/9.2 and passed others.

[kaiwk]

I also add an api called new_from_arc_buffer, so maybe font-kit can benefit from it : )

[bors-servo]

:umbrella: The latest upstream changes (presumably #485) made this pull request unmergeable. Please resolve the merge conflicts.