win32: use the version major libvlc number in the DLL name

This will avoid loading incompatible DLLs automatically.

Windows app can still link with libvlc.lib and libvlc.dll.a. These names are not versioned, they point to the versioned DLL.

Separate libvlc and libvlccore DLL files as they don't describe the same thing.

Follow-up to !2883 (merged)