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/Lib/test/test_embed.py b/Lib/test/test_embed.py
index fe47289..174892a 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -365,7 +365,7 @@
         'program_name': GET_DEFAULT_CONFIG,
         'parse_argv': 0,
         'argv': [""],
-        '_orig_argv': [],
+        'orig_argv': [],
 
         'xoptions': [],
         'warnoptions': [],
@@ -739,11 +739,11 @@
             'pycache_prefix': 'conf_pycache_prefix',
             'program_name': './conf_program_name',
             'argv': ['-c', 'arg2'],
-            '_orig_argv': ['python3',
-                           '-W', 'cmdline_warnoption',
-                           '-X', 'cmdline_xoption',
-                           '-c', 'pass',
-                           'arg2'],
+            'orig_argv': ['python3',
+                          '-W', 'cmdline_warnoption',
+                          '-X', 'cmdline_xoption',
+                          '-c', 'pass',
+                          'arg2'],
             'parse_argv': 1,
             'xoptions': [
                 'config_xoption1=3',
@@ -874,7 +874,7 @@
         }
         config = {
             'argv': ['script.py'],
-            '_orig_argv': ['python3', '-X', 'dev', 'script.py'],
+            'orig_argv': ['python3', '-X', 'dev', 'script.py'],
             'run_filename': os.path.abspath('script.py'),
             'dev_mode': 1,
             'faulthandler': 1,
@@ -896,7 +896,7 @@
                "script.py"]
         config = {
             'argv': argv,
-            '_orig_argv': argv,
+            'orig_argv': argv,
             'isolated': 0,
         }
         self.check_all_configs("test_preinit_dont_parse_argv", config, preconfig,
@@ -975,9 +975,9 @@
                 'ignore:::sysadd_warnoption',
                 'ignore:::config_warnoption',
             ],
-            '_orig_argv': ['python3',
-                           '-W', 'ignore:::cmdline_warnoption',
-                           '-X', 'cmdline_xoption'],
+            'orig_argv': ['python3',
+                          '-W', 'ignore:::cmdline_warnoption',
+                          '-X', 'cmdline_xoption'],
         }
         self.check_all_configs("test_init_sys_add", config, api=API_PYTHON)
 
@@ -986,7 +986,7 @@
                 'print(json.dumps(_testinternalcapi.get_configs()))')
         config = {
             'argv': ['-c', 'arg2'],
-            '_orig_argv': ['python3', '-c', code, 'arg2'],
+            'orig_argv': ['python3', '-c', code, 'arg2'],
             'program_name': './python3',
             'run_command': code + '\n',
             'parse_argv': 1,
@@ -998,9 +998,9 @@
                 'print(json.dumps(_testinternalcapi.get_configs()))')
         config = {
             'argv': ['-c', 'arg2'],
-            '_orig_argv': ['python3',
-                           '-c', code,
-                           'arg2'],
+            'orig_argv': ['python3',
+                          '-c', code,
+                          'arg2'],
             'program_name': './python3',
             'run_command': code + '\n',
             'parse_argv': 1,
@@ -1014,7 +1014,7 @@
         config = {
             'parse_argv': 1,
             'argv': ['-c', 'arg1', '-v', 'arg3'],
-            '_orig_argv': ['./argv0', '-E', '-c', 'pass', 'arg1', '-v', 'arg3'],
+            'orig_argv': ['./argv0', '-E', '-c', 'pass', 'arg1', '-v', 'arg3'],
             'program_name': './argv0',
             'run_command': 'pass\n',
             'use_environment': 0,
@@ -1028,7 +1028,7 @@
         config = {
             'parse_argv': 0,
             'argv': ['./argv0', '-E', '-c', 'pass', 'arg1', '-v', 'arg3'],
-            '_orig_argv': ['./argv0', '-E', '-c', 'pass', 'arg1', '-v', 'arg3'],
+            'orig_argv': ['./argv0', '-E', '-c', 'pass', 'arg1', '-v', 'arg3'],
             'program_name': './argv0',
         }
         self.check_all_configs("test_init_dont_parse_argv", config, pre_config,
@@ -1316,9 +1316,9 @@
             'faulthandler': 1,
             'bytes_warning': 1,
             'warnoptions': warnoptions,
-            '_orig_argv': ['python3',
-                           '-Wignore:::cmdline1',
-                           '-Wignore:::cmdline2'],
+            'orig_argv': ['python3',
+                          '-Wignore:::cmdline1',
+                          '-Wignore:::cmdline2'],
         }
         self.check_all_configs("test_init_warnoptions", config, preconfig,
                                api=API_PYTHON)