Only accept fractional point sizes and numeric weights via wxFont ctor
using wxFontInfo and avoid having specific ctor/Create() overloads for
the different combinations of font properties: this is not portable (as
these ctors don't exist in the other ports) and unsustainable due to the
very real potential of combinatorial explosion as more properties are
added.
As a side-effect, fix support for stricken-through fonts under Mac,
which was broken, by adding the missing wxFontInfo::IsStrikethrough()
call.
24c83625f6