Reorganize upb file structure

This change moves almost everything in the `upb/` directory up one level, so
that for example `upb/upb/generated_code_support.h` becomes just
`upb/generated_code_support.h`. The only exceptions I made to this were that I
left `upb/cmake` and `upb/BUILD` where they are, mostly because that avoids
conflict with other files and the current locations seem reasonable for now.

The `python/` directory is a little bit of a challenge because we had to merge
the existing directory there with `upb/python/`. I made `upb/python/BUILD` into
the BUILD file for the merged directory, and it effectively loads the contents
of the other BUILD file via `python/build_targets.bzl`, but I plan to clean
this up soon.

PiperOrigin-RevId: 568651768

python/repeated.h

@@ -0,0 +1,72 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2023 Google LLC.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google LLC nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef PYUPB_REPEATED_H__
+#define PYUPB_REPEATED_H__
+
+#include <stdbool.h>
+
+#include "python/python_api.h"
+#include "upb/reflection/def.h"
+
+// Creates a new repeated field stub for field `f` of message object `parent`.
+// Precondition: `parent` must be a stub.
+PyObject* PyUpb_RepeatedContainer_NewStub(PyObject* parent,
+                                          const upb_FieldDef* f,
+                                          PyObject* arena);
+
+// Returns a repeated field object wrapping `arr`, of field type `f`, which
+// must be on `arena`.  If an existing wrapper object exists, it will be
+// returned, otherwise a new object will be created.  The caller always owns a
+// ref on the returned value.
+PyObject* PyUpb_RepeatedContainer_GetOrCreateWrapper(upb_Array* arr,
+                                                     const upb_FieldDef* f,
+                                                     PyObject* arena);
+
+// Reifies a repeated field stub to point to the concrete data in `arr`.
+// If `arr` is NULL, an appropriate empty array will be constructed.
+void PyUpb_RepeatedContainer_Reify(PyObject* self, upb_Array* arr);
+
+// Reifies this repeated object if it is not already reified.
+upb_Array* PyUpb_RepeatedContainer_EnsureReified(PyObject* self);
+
+// Implements repeated_field.extend(iterable).  `_self` must be a repeated
+// field (either repeated composite or repeated scalar).
+PyObject* PyUpb_RepeatedContainer_Extend(PyObject* _self, PyObject* value);
+
+// Implements repeated_field.add(initial_values).  `_self` must be a repeated
+// composite field.
+PyObject* PyUpb_RepeatedCompositeContainer_Add(PyObject* _self, PyObject* args,
+                                               PyObject* kwargs);
+
+// Module-level init.
+bool PyUpb_Repeated_Init(PyObject* m);
+
+#endif  // PYUPB_REPEATED_H__