[Windows] restrict DLL load to system libraries

As the docs for NewLazyDLL indicate [0], it is vulnerable to DLL preload
attacks when the path provided is not absolute. Since we're only loading
a system library here, we can safely restrict the search to the system32
directory and eliminate this issue.

[0] https://pkg.go.dev/golang.org/x/sys@v0.29.0/windows#NewLazyDLL