bpo-40939: Rename PyPegen* functions to PyParser* (GH-21016)

Rename PyPegen* functions to PyParser*, so that we can remove the
old set of PyParser* functions that were using the old parser.

diff --git a/Parser/peg_api.c b/Parser/peg_api.c
index b947c78..8381d5e 100644
--- a/Parser/peg_api.c
+++ b/Parser/peg_api.c
@@ -1,23 +1,23 @@
-#include "pegen_interface.h"
+#include "parser_interface.h"
 
 #include "tokenizer.h"
 #include "pegen.h"
 
 mod_ty
-PyPegen_ASTFromString(const char *str, const char *filename, int mode,
+PyParser_ASTFromString(const char *str, const char *filename, int mode,
                       PyCompilerFlags *flags, PyArena *arena)
 {
     PyObject *filename_ob = PyUnicode_FromString(filename);
     if (filename_ob == NULL) {
         return NULL;
     }
-    mod_ty result = PyPegen_ASTFromStringObject(str, filename_ob, mode, flags, arena);
+    mod_ty result = PyParser_ASTFromStringObject(str, filename_ob, mode, flags, arena);
     Py_XDECREF(filename_ob);
     return result;
 }
 
 mod_ty
-PyPegen_ASTFromStringObject(const char *str, PyObject* filename, int mode,
+PyParser_ASTFromStringObject(const char *str, PyObject* filename, int mode,
                             PyCompilerFlags *flags, PyArena *arena)
 {
     if (PySys_Audit("compile", "yO", str, filename) < 0) {
@@ -29,7 +29,7 @@
 }
 
 mod_ty
-PyPegen_ASTFromFilename(const char *filename, int mode, PyCompilerFlags *flags, PyArena *arena)
+PyParser_ASTFromFilename(const char *filename, int mode, PyCompilerFlags *flags, PyArena *arena)
 {
     PyObject *filename_ob = PyUnicode_FromString(filename);
     if (filename_ob == NULL) {
@@ -42,8 +42,23 @@
 }
 
 mod_ty
-PyPegen_ASTFromFileObject(FILE *fp, PyObject *filename_ob, int mode,
-                          const char *enc, const char *ps1, const char* ps2,
+PyParser_ASTFromFile(FILE *fp, const char *filename, const char *enc,
+                    int mode, const char *ps1, const char* ps2,
+                    PyCompilerFlags *flags, int *errcode, PyArena *arena)
+{
+    PyObject *filename_ob = PyUnicode_FromString(filename);
+    if (filename_ob == NULL) {
+        return NULL;
+    }
+    mod_ty result = PyParser_ASTFromFileObject(fp, filename_ob, enc, mode,
+                                              ps1, ps2, flags, errcode, arena);
+    Py_XDECREF(filename_ob);
+    return result;
+}
+
+mod_ty
+PyParser_ASTFromFileObject(FILE *fp, PyObject *filename_ob, const char *enc,
+                          int mode, const char *ps1, const char* ps2,
                           PyCompilerFlags *flags, int *errcode, PyArena *arena)
 {
     if (PySys_Audit("compile", "OO", Py_None, filename_ob) < 0) {