bpo-43244: Add pycore_compile.h header file (GH-25000)

Remove the compiler functions using "struct _mod" type, because the
public AST C API was removed:

* PyAST_Compile()
* PyAST_CompileEx()
* PyAST_CompileObject()
* PyFuture_FromAST()
* PyFuture_FromASTObject()

These functions were undocumented and excluded from the limited C API.

Rename functions:

* PyAST_CompileObject() => _PyAST_Compile()
* PyFuture_FromASTObject() => _PyFuture_FromAST()

Moreover, _PyFuture_FromAST() is no longer exported (replace
PyAPI_FUNC() with extern). _PyAST_Compile() remains exported for
test_peg_generator.

Remove also compatibility functions:

* PyAST_Compile()
* PyAST_CompileEx()
* PyFuture_FromAST()

Python/future.c

@@ -116,7 +116,7 @@ future_parse(PyFutureFeatures *ff, mod_ty mod, PyObject *filename)
 
 
 PyFutureFeatures *
-PyFuture_FromASTObject(mod_ty mod, PyObject *filename)
+_PyFuture_FromAST(mod_ty mod, PyObject *filename)
 {
     PyFutureFeatures *ff;
 
@@ -134,18 +134,3 @@ PyFuture_FromASTObject(mod_ty mod, PyObject *filename)
     }
     return ff;
 }
-
-
-PyFutureFeatures *
-PyFuture_FromAST(mod_ty mod, const char *filename_str)
-{
-    PyFutureFeatures *ff;
-    PyObject *filename;
-
-    filename = PyUnicode_DecodeFSDefault(filename_str);
-    if (filename == NULL)
-        return NULL;
-    ff = PyFuture_FromASTObject(mod, filename);
-    Py_DECREF(filename);
-    return ff;
-}