hooks: add hook for toga_cocoa

Add hook for `toga_cocoa` (the macOS backend for `toga`) to collect
images (default icon, camera icon) from `resources`.

_pyinstaller_hooks_contrib/stdhooks/hook-toga_cocoa.py

@@ -0,0 +1,16 @@
+# ------------------------------------------------------------------
+# Copyright (c) 2024 PyInstaller Development Team.
+#
+# This file is distributed under the terms of the GNU General Public
+# License (version 2.0 or later).
+#
+# The full license is available in LICENSE, distributed with
+# this software.
+#
+# SPDX-License-Identifier: GPL-2.0-or-later
+# ------------------------------------------------------------------
+
+from PyInstaller.utils.hooks import collect_data_files
+
+# Collect icons from `resources`.
+datas = collect_data_files('toga_cocoa')