Add non-vararg wxFileTypeInfo ctor and various setters.

Add non-vararg wxFileTypeInfo ctor and various setters.

This allows to create wxFileTypeInfo objects in a more readable even if more
verbose way.

This should also incidentally fix the unit tests compilation with VC6 which
seems to have some existential troubles with the vararg ctor in debug DLL
build (only). Using the non-vararg ctor should hopefully make it happy and let
the unit tests pass with this compiler.

Also document wxFileTypeInfo class which wasn't documented at all.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65707 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775