cmSystemTools: Restore FindProgram look-up of on-disk case on Windows

KWSys's `FindProgram` no longer looks up the actual case on disk.  This
behavior change was inherited from the change to `CollapseFullPath`.
Extend commit 773b75e4ed (cmake: Explicitly look up on-disk case of
input paths on Windows, 2024-10-23, v4.0.0-rc1~589^2) to cover this by
wrapping `FindProgram` in a CMake-specific layer.

Issue: #20214