cmSystemTools: Revert GetRealPath implementation on Windows
The use of uv_fs_realpath
introduced by commit 640709e7 (in !1202 (merged)) causes
subst
drives to be expanded on Windows, breaking existing use cases.
Revert its use until an alternative implementation can be chosen.
Preserve the behavior introduced by commit 393e0fbe (also in !1202 (merged)) by retaining use of uv_fs_realpath
in a function of
a different name.
Fixes: #18033 (closed)
Issue: #17206