Check for freetype2 version when PangoFT is used

Check for freetype2 version when PangoFT is used

Check for freetype2 version, because pangoft works with any version
(pangoft availability does not indicate that ft2 is new enough), unlike
GTK.

On Windows, since pangoft is optional, we check for the presence of
freetype2 .pc file first after finding that we have pangoft, and then
check for FT_Get_Var_Design_Coordinates() manually by looking for the
freetype headers and .lib first, and then looking for the presence of
that symbol, since freetype2's Visual Studio build system does not
generate a .pc file for us.

https://bugzilla.gnome.org/show_bug.cgi?id=773299