bpo-35081: Move bytes_methods.h to the internal C API (GH-18492)

Move the bytes_methods.h header file to the internal C API as
pycore_bytes_methods.h: it only contains private symbols (prefixed by
"_Py"), except of the PyDoc_STRVAR_shared() macro.
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index a3fc35c..d396435 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -2,11 +2,11 @@
 
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
+#include "pycore_bytes_methods.h"
 #include "pycore_object.h"
 #include "pycore_pymem.h"
 #include "pycore_pystate.h"
 #include "structmember.h"
-#include "bytes_methods.h"
 #include "bytesobject.h"
 #include "pystrhex.h"
 
diff --git a/Objects/bytes_methods.c b/Objects/bytes_methods.c
index db030be..a4b3868 100644
--- a/Objects/bytes_methods.c
+++ b/Objects/bytes_methods.c
@@ -1,6 +1,6 @@
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
-#include "bytes_methods.h"
+#include "pycore_bytes_methods.h"
 
 PyDoc_STRVAR_shared(_Py_isspace__doc__,
 "B.isspace() -> bool\n\
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index df3edda..bd8af72 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -3,11 +3,11 @@
 #define PY_SSIZE_T_CLEAN
 
 #include "Python.h"
+#include "pycore_bytes_methods.h"
 #include "pycore_object.h"
 #include "pycore_pymem.h"
 #include "pycore_pystate.h"
 
-#include "bytes_methods.h"
 #include "pystrhex.h"
 #include <stddef.h>
 
diff --git a/Objects/stringlib/ctype.h b/Objects/stringlib/ctype.h
index 843cfa2..9b319b0 100644
--- a/Objects/stringlib/ctype.h
+++ b/Objects/stringlib/ctype.h
@@ -2,7 +2,7 @@
 # error "ctype.h only compatible with byte-wise strings"
 #endif
 
-#include "bytes_methods.h"
+#include "pycore_bytes_methods.h"
 
 static PyObject*
 stringlib_isspace(PyObject *self, PyObject *Py_UNUSED(ignored))
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 8470e41..11fa1fb5 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -40,6 +40,7 @@
 
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
+#include "pycore_bytes_methods.h"
 #include "pycore_fileutils.h"
 #include "pycore_initconfig.h"
 #include "pycore_object.h"
@@ -47,7 +48,6 @@
 #include "pycore_pylifecycle.h"
 #include "pycore_pystate.h"
 #include "ucnhash.h"
-#include "bytes_methods.h"
 #include "stringlib/eq.h"
 
 #ifdef MS_WINDOWS