bpo-23427: Add sys.orig_argv attribute (GH-20729)

Add sys.orig_argv attribute: the list of the original command line
arguments passed to the Python executable.

Rename also PyConfig._orig_argv to PyConfig.orig_argv and
document it.
diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index 880f252..d201d70 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -66,6 +66,8 @@
    To loop over the standard input, or the list of files given on the
    command line, see the :mod:`fileinput` module.
 
+   See also :data:`sys.orig_argv`.
+
    .. note::
       On Unix, command line arguments are passed by bytes from OS.  Python decodes
       them with filesystem encoding and "surrogateescape" error handler.
@@ -1037,6 +1039,16 @@
    deleting essential items from the dictionary may cause Python to fail.
 
 
+.. data:: orig_argv
+
+   The list of the original command line arguments passed to the Python
+   executable.
+
+   See also :data:`sys.argv`.
+
+   .. versionadded:: 3.10
+
+
 .. data:: path
 
    .. index:: triple: module; search; path