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()
diff --git a/Python/symtable.c b/Python/symtable.c
index 7887440..a149e28 100644
--- a/Python/symtable.c
+++ b/Python/symtable.c
@@ -1,8 +1,9 @@
 #include "Python.h"
 #include "pycore_ast.h"           // identifier, stmt_ty
+#undef Yield   /* undefine macro conflicting with <winbase.h> */
+#include "pycore_compile.h"       // _Py_Mangle()
 #include "pycore_pystate.h"       // _PyThreadState_GET()
 #include "pycore_symtable.h"      // PySTEntryObject
-#undef Yield   /* undefine macro conflicting with <winbase.h> */
 #include "structmember.h"         // PyMemberDef
 
 /* error strings used for warnings */