gh-88745: Add _winapi.CopyFile2 and update shutil.copy2 to use it (GH-105055)

(cherry picked from commit cda1bd3c9d)

Co-authored-by: Steve Dower <steve.dower@python.org>

Lib/shutil.py

@@ -42,6 +42,8 @@ elif _WINDOWS:
 
 if sys.platform == 'win32':
     import _winapi
+else:
+    _winapi = None
 
 COPY_BUFSIZE = 1024 * 1024 if _WINDOWS else 64 * 1024
 # This should never be removed, see rationale in:
@@ -435,6 +437,29 @@ def copy2(src, dst, *, follow_symlinks=True):
     """
     if os.path.isdir(dst):
         dst = os.path.join(dst, os.path.basename(src))
+
+    if hasattr(_winapi, "CopyFile2"):
+        src_ = os.fsdecode(src)
+        dst_ = os.fsdecode(dst)
+        flags = _winapi.COPY_FILE_ALLOW_DECRYPTED_DESTINATION # for compat
+        if not follow_symlinks:
+            flags |= _winapi.COPY_FILE_COPY_SYMLINK
+        try:
+            _winapi.CopyFile2(src_, dst_, flags)
+            return dst
+        except OSError as exc:
+            if (exc.winerror == _winapi.ERROR_PRIVILEGE_NOT_HELD
+                and not follow_symlinks):
+                # Likely encountered a symlink we aren't allowed to create.
+                # Fall back on the old code
+                pass
+            elif exc.winerror == _winapi.ERROR_ACCESS_DENIED:
+                # Possibly encountered a hidden or readonly file we can't
+                # overwrite. Fall back on old code
+                pass
+            else:
+                raise
+
     copyfile(src, dst, follow_symlinks=follow_symlinks)
     copystat(src, dst, follow_symlinks=follow_symlinks)
     return dst