GH-119169: Implement pathlib.Path.walk() using os.walk() (#119573)

For silly reasons, pathlib's generic implementation of `walk()` currently
resides in `glob._Globber`. This commit moves it into
`pathlib._abc.PathBase.walk()` where it really belongs, and makes
`pathlib.Path.walk()` call `os.walk()`.

Lib/pathlib/_abc.py

@@ -621,7 +621,37 @@ class PathBase(PurePathBase):
 
     def walk(self, top_down=True, on_error=None, follow_symlinks=False):
         """Walk the directory tree from this directory, similar to os.walk()."""
-        return self._globber.walk(self, top_down, on_error, follow_symlinks)
+        paths = [self]
+        while paths:
+            path = paths.pop()
+            if isinstance(path, tuple):
+                yield path
+                continue
+            dirnames = []
+            filenames = []
+            if not top_down:
+                paths.append((path, dirnames, filenames))
+            try:
+                for child in path.iterdir():
+                    try:
+                        if child.is_dir(follow_symlinks=follow_symlinks):
+                            if not top_down:
+                                paths.append(child)
+                            dirnames.append(child.name)
+                        else:
+                            filenames.append(child.name)
+                    except OSError:
+                        filenames.append(child.name)
+            except OSError as error:
+                if on_error is not None:
+                    on_error(error)
+                if not top_down:
+                    while not isinstance(paths.pop(), tuple):
+                        pass
+                continue
+            if top_down:
+                yield path, dirnames, filenames
+                paths += [path.joinpath(d) for d in reversed(dirnames)]
 
     def absolute(self):
         """Return an absolute version of this path