bpo-36142: Remove _PyMain structure (GH-12120)

* Move fields from _PyMain to _PyCoreConfig:

  * skip_first_line
  * run_command
  * run_module
  * run_filename

* Replace _PyMain.stdin_is_interactive with a new
  stdin_is_interactive(config) function
* Rename _PyMain to _PyArgv. Add "const _PyArgv *args" field
  to _PyCmdline.

Include/cpython/coreconfig.h

@@ -276,7 +276,19 @@ typedef struct {
     int legacy_windows_stdio;
 #endif
 
-    /* --- Private fields -------- */
+    /* --- Parameter only used by Py_Main() ---------- */
+
+    /* Skip the first line of the source ('run_filename' parameter), allowing use of non-Unix forms of
+       "#!cmd".  This is intended for a DOS specific hack only.
+
+       Set by the -x command line option. */
+    int skip_source_first_line;
+
+    wchar_t *run_command;   /* -c command line argument */
+    wchar_t *run_module;    /* -m command line argument */
+    wchar_t *run_filename;  /* Trailing command line argument without -c or -m */
+
+    /* --- Private fields ---------------------------- */
 
     /* Install importlib? If set to 0, importlib is not initialized at all.
        Needed by freeze_importlib. */

Lib/test/test_embed.py

@@ -322,6 +322,11 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         'stdio_encoding': GET_DEFAULT_CONFIG,
         'stdio_errors': GET_DEFAULT_CONFIG,
 
+        'skip_source_first_line': 0,
+        'run_command': None,
+        'run_module': None,
+        'run_filename': None,
+
         '_install_importlib': 1,
         '_check_hash_pycs_mode': 'default',
         '_frozen': 0,

Python/coreconfig.c

@@ -424,6 +424,10 @@ _PyCoreConfig_Copy(_PyCoreConfig *config, const _PyCoreConfig *config2)
     COPY_ATTR(legacy_windows_fs_encoding);
     COPY_ATTR(legacy_windows_stdio);
 #endif
+    COPY_ATTR(skip_source_first_line);
+    COPY_WSTR_ATTR(run_command);
+    COPY_WSTR_ATTR(run_module);
+    COPY_WSTR_ATTR(run_filename);
     COPY_ATTR(_check_hash_pycs_mode);
     COPY_ATTR(_frozen);
 
@@ -1559,6 +1563,10 @@ _PyCoreConfig_AsDict(const _PyCoreConfig *config)
     SET_ITEM_INT(legacy_windows_fs_encoding);
     SET_ITEM_INT(legacy_windows_stdio);
 #endif
+    SET_ITEM_INT(skip_source_first_line);
+    SET_ITEM_WSTR(run_command);
+    SET_ITEM_WSTR(run_module);
+    SET_ITEM_WSTR(run_filename);
     SET_ITEM_INT(_install_importlib);
     SET_ITEM_STR(_check_hash_pycs_mode);
     SET_ITEM_INT(_frozen);