pythongh-107801: Improve the accuracy of os.lseek docs

- name the last parameter *whence*, like it is for seek() methods on
  file objects
- add param docstrings
- structure the valid *whence* values as a list

Doc/library/os.rst

@@ -1163,13 +1163,16 @@ as internal buffering of data.
    .. versionadded:: 3.11
 
 
-.. function:: lseek(fd, pos, how, /)
+.. function:: lseek(fd, pos, whence, /)
 
    Set the current position of file descriptor *fd* to position *pos*, modified
-   by *how*: :const:`SEEK_SET` or ``0`` to set the position relative to the
-   beginning of the file; :const:`SEEK_CUR` or ``1`` to set it relative to the
-   current position; :const:`SEEK_END` or ``2`` to set it relative to the end of
-   the file. Return the new cursor position in bytes, starting from the beginning.
+   by *whence*, and return the new position in bytes, relative to
+   the start of the file.
+   Valid values for *whence* are:
+
+   * :const:`SEEK_SET` or ``0`` -- set *pos* relative to the beginning of the file
+   * :const:`SEEK_CUR` or ``1`` -- set *pos* relative to the current file position
+   * :const:`SEEK_END` or ``2`` -- set *pos* relative to the end of the file
 
 
 .. data:: SEEK_SET

Modules/posixmodule.c

@@ -10422,14 +10422,19 @@ os_lockf_impl(PyObject *module, int fd, int command, Py_off_t length)
 os.lseek -> Py_off_t
 
     fd: int
+        An open file descriptor, as returned by os.open().
     position: Py_off_t
-    how: int
+        Position, interpreted relative to 'whence'.
+    whence as how: int
+        The relative position to seek from. Valid values are:
+        - SEEK_SET: seek from the start of the file.
+        - SEEK_CUR: seek from the current file position.
+        - SEEK_END: seek from the end of the file.
     /
 
-Set the position of a file descriptor.  Return the new position.
+Set the position of a file descriptor, and return the new position.
 
-Return the new cursor position in number of bytes
-relative to the beginning of the file.
+The return value is the number of bytes relative to the beginning of the file.
 [clinic start generated code]*/
 
 static Py_off_t