CPack/NuGet: Restore component packaging on Windows

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
38 jobs for !7280 with bug/22489 in 4 minutes and 53 seconds (queued for 2 seconds)
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