bpo-36763: Make Py_BytesMain() public (GH-15532)

Declare Py_BytesMain() in Include/pylifecycle.h, rather in
Include/internal/pycore_pylifecycle.h.
diff --git a/Include/pylifecycle.h b/Include/pylifecycle.h
index 1df114a..c5368b3 100644
--- a/Include/pylifecycle.h
+++ b/Include/pylifecycle.h
@@ -32,6 +32,8 @@
 /* Bootstrap __main__ (defined in Modules/main.c) */
 PyAPI_FUNC(int) Py_Main(int argc, wchar_t **argv);
 
+PyAPI_FUNC(int) Py_BytesMain(int argc, char **argv);
+
 /* In pathconfig.c */
 PyAPI_FUNC(void) Py_SetProgramName(const wchar_t *);
 PyAPI_FUNC(wchar_t *) Py_GetProgramName(void);