CPack/NuGet: Restore component packaging on Windows

The change from `\` to `/` in commit dade75509f (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
diff --git a/Modules/Internal/CPack/CPackNuGet.cmake b/Modules/Internal/CPack/CPackNuGet.cmake
index fb363f4..056d025 100644
--- a/Modules/Internal/CPack/CPackNuGet.cmake
+++ b/Modules/Internal/CPack/CPackNuGet.cmake
@@ -332,7 +332,9 @@
 function(_cpack_nuget_make_files_tag)
     set(_files)
     foreach(_comp IN LISTS ARGN)
-        string(APPEND _files "        <file src=\"${_comp}/**\" target=\".\" />\n")
+        cmake_path(APPEND _comp "**")
+        cmake_path(NATIVE_PATH _comp _comp)
+        string(APPEND _files "        <file src=\"${_comp}\" target=\".\" />\n")
     endforeach()
     set(_CPACK_NUGET_FILES_TAG "<files>\n${_files}    </files>" PARENT_SCOPE)
 endfunction()