Alex Turbov authored May 18, 2022 and Brad King committed May 18, 2022

The change from `\` to `/` in commit dade7550 (CPack/NuGet: Fix nuspec
file generation for UNIX-style OS, 2020-12-21, v3.20.0-rc1~243^2) does
not work on Windows.  Use `cmake_path` to form a path to an image
directory with preinstalled files.

Fixes: #22489