bpo-40334: Make the PyPegen* and PyParser* APIs more consistent (GH-19839)

This commit makes both APIs more consistent by doing the following:
- Remove the `PyPegen_CodeObjectFrom*` functions, which weren't used 
  and will probably not be needed. Functions like `Py_CompileStringObject`
  can be used instead.
- Include a `const char *filename` parameter in `PyPegen_ASTFromString`.
- Rename `PyPegen_ASTFromFile` to `PyPegen_ASTFromFilename`, because
  its signature is not the same with `PyParser_ASTFromFile`.
diff --git a/Include/internal/pegen_interface.h b/Include/internal/pegen_interface.h
index adff731..ee4c77e 100644
--- a/Include/internal/pegen_interface.h
+++ b/Include/internal/pegen_interface.h
@@ -11,25 +11,34 @@
 #include "Python.h"
 #include "Python-ast.h"
 
-PyAPI_FUNC(mod_ty) PyPegen_ASTFromFile(const char *filename, int mode, PyCompilerFlags*, PyArena *arena);
-PyAPI_FUNC(mod_ty) PyPegen_ASTFromString(const char *str, int mode, PyCompilerFlags *flags,
-                                         PyArena *arena);
-PyAPI_FUNC(mod_ty) PyPegen_ASTFromStringObject(const char *str, PyObject* filename, int mode,
-                                               PyCompilerFlags *flags, PyArena *arena);
-PyAPI_FUNC(mod_ty) PyPegen_ASTFromFileObject(FILE *fp, PyObject *filename_ob,
-                                             int mode, const char *enc, const char *ps1,
-                                             const char *ps2, PyCompilerFlags *flags,
-                                             int *errcode, PyArena *arena);
-PyAPI_FUNC(PyCodeObject *) PyPegen_CodeObjectFromFile(const char *filename, int mode, PyCompilerFlags *flags);
-PyAPI_FUNC(PyCodeObject *) PyPegen_CodeObjectFromString(const char *str, int mode,
-                                                        PyCompilerFlags *flags);
-PyAPI_FUNC(PyCodeObject *) PyPegen_CodeObjectFromFileObject(FILE *, PyObject *filename_ob,
-                                                            int mode,
-                                                            const char *ps1,
-                                                            const char *ps2,
-                                                            PyCompilerFlags *flags,
-                                                            const char *enc,
-                                                            int *errcode);
+PyAPI_FUNC(mod_ty) PyPegen_ASTFromString(
+    const char *str,
+    const char *filename,
+    int mode,
+    PyCompilerFlags *flags,
+    PyArena *arena);
+PyAPI_FUNC(mod_ty) PyPegen_ASTFromStringObject(
+    const char *str,
+    PyObject* filename,
+    int mode,
+    PyCompilerFlags *flags,
+    PyArena *arena);
+PyAPI_FUNC(mod_ty) PyPegen_ASTFromFileObject(
+    FILE *fp,
+    PyObject *filename_ob,
+    int mode,
+    const char *enc,
+    const char *ps1,
+    const char *ps2,
+    PyCompilerFlags *flags,
+    int *errcode,
+    PyArena *arena);
+PyAPI_FUNC(mod_ty) PyPegen_ASTFromFilename(
+    const char *filename,
+    int mode,
+    PyCompilerFlags *flags,
+    PyArena *arena);
+
 
 #ifdef __cplusplus
 }