ThemeReader.cpp can be updated for VC7

There is a comment near the top of src/windows/native/sun/windows/ThemeReader.cpp mentioning that changes should be made once the build changes from using VC6 to VC7. Well, the JDK is now being built with VC7, so we should now be able to #include uxtheme.h, remove some of the copied typedefs and #defines, etc.

It may also be possible to simply link to uxtheme.dll instead of using LoadLibrary() & GetProcAddress() for the theme-related functions that we use. Whether or not this is a good idea will require further investigation. It could be that there are new APIs in Vista for which we will have to use GetProcAddress() anyway. There may also be a performance difference between opening the .dll ourselves and just letting the dynamic linker take care of things for us. And of course, we need to make sure we are able to run on older versions of Windows that we still support, as well as building on the official build platform, which at the moment I believe is still Windows 2000.