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/ast_opt.c b/Python/ast_opt.c
index c76b428..64fa067 100644
--- a/Python/ast_opt.c
+++ b/Python/ast_opt.c
@@ -1,6 +1,7 @@
 /* AST Optimizer */
 #include "Python.h"
 #include "pycore_ast.h"           // _PyAST_GetDocString()
+#include "pycore_compile.h"       // _PyASTOptimizeState
 
 
 static int