bpo-40421: Add pyframe.h header file (GH-19755)

Add a new separated pyframe.h header file of the PyFrame public C
API: it is included by Python.h.

Add PyFrame_GetLineNumber() to the limited C API.

Replace "struct _frame" with "PyFrameObject" in header files.
PyFrameObject is now defined as struct _frame by pyframe.h which is
included early enough in Python.h.
diff --git a/Include/cpython/ceval.h b/Include/cpython/ceval.h
index 020f787..e1922a6 100644
--- a/Include/cpython/ceval.h
+++ b/Include/cpython/ceval.h
@@ -23,7 +23,7 @@
    flag was set, else return 0. */
 PyAPI_FUNC(int) PyEval_MergeCompilerFlags(PyCompilerFlags *cf);
 
-PyAPI_FUNC(PyObject *) _PyEval_EvalFrameDefault(PyThreadState *tstate, struct _frame *f, int exc);
+PyAPI_FUNC(PyObject *) _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int exc);
 
 PyAPI_FUNC(void) _PyEval_SetSwitchInterval(unsigned long microseconds);
 PyAPI_FUNC(unsigned long) _PyEval_GetSwitchInterval(void);
diff --git a/Include/cpython/frameobject.h b/Include/cpython/frameobject.h
index 4ced967..e819cef 100644
--- a/Include/cpython/frameobject.h
+++ b/Include/cpython/frameobject.h
@@ -14,7 +14,7 @@
     int b_level;                /* value stack level to pop to */
 } PyTryBlock;
 
-typedef struct _frame {
+struct _frame {
     PyObject_VAR_HEAD
     struct _frame *f_back;      /* previous frame, or NULL */
     PyCodeObject *f_code;       /* code segment */
@@ -44,7 +44,7 @@
     char f_executing;           /* whether the frame is still executing */
     PyTryBlock f_blockstack[CO_MAXBLOCKS]; /* for try and loop blocks */
     PyObject *f_localsplus[1];  /* locals+stack, dynamically sized */
-} PyFrameObject;
+};
 
 
 /* Standard object interface */
@@ -79,9 +79,6 @@
 
 PyAPI_FUNC(void) _PyFrame_DebugMallocStats(FILE *out);
 
-/* Return the line of code the frame is currently executing. */
-PyAPI_FUNC(int) PyFrame_GetLineNumber(PyFrameObject *);
-
 #ifdef __cplusplus
 }
 #endif
diff --git a/Include/cpython/pystate.h b/Include/cpython/pystate.h
index 9b28f66..f292da1 100644
--- a/Include/cpython/pystate.h
+++ b/Include/cpython/pystate.h
@@ -16,7 +16,7 @@
 /* State unique per thread */
 
 /* Py_tracefunc return -1 when raising an exception, or 0 for success. */
-typedef int (*Py_tracefunc)(PyObject *, struct _frame *, int, PyObject *);
+typedef int (*Py_tracefunc)(PyObject *, PyFrameObject *, int, PyObject *);
 
 /* The following values are used for 'what' for tracefunc functions
  *
@@ -56,7 +56,7 @@
     PyInterpreterState *interp;
 
     /* Borrowed reference to the current frame (it can be NULL) */
-    struct _frame *frame;
+    PyFrameObject *frame;
     int recursion_depth;
     char overflowed; /* The stack has overflowed. Allow 50 more calls
                         to handle the runtime error. */
@@ -184,7 +184,7 @@
 
 /* Frame evaluation API */
 
-typedef PyObject* (*_PyFrameEvalFunction)(PyThreadState *tstate, struct _frame *, int);
+typedef PyObject* (*_PyFrameEvalFunction)(PyThreadState *tstate, PyFrameObject *, int);
 
 PyAPI_FUNC(_PyFrameEvalFunction) _PyInterpreterState_GetEvalFrameFunc(
     PyInterpreterState *interp);
diff --git a/Include/cpython/traceback.h b/Include/cpython/traceback.h
index 746097d..837470c 100644
--- a/Include/cpython/traceback.h
+++ b/Include/cpython/traceback.h
@@ -9,7 +9,7 @@
 typedef struct _traceback {
     PyObject_HEAD
     struct _traceback *tb_next;
-    struct _frame *tb_frame;
+    PyFrameObject *tb_frame;
     int tb_lasti;
     int tb_lineno;
 } PyTracebackObject;