PyAPI: temporary context override support

Support a way to temporarily override the context from Python.

- Added method `Context.temp_override` context manager.
- Special support for windowing variables "window", "area" and "region",
  other context members such as "active_object".
- Nesting context overrides is supported.
- Previous windowing members are restored when the context exists unless
  they have been removed.
- Overriding context members by passing a dictionary into operators in
  `bpy.ops` has been deprecated and warns when used.

This allows the window in a newly loaded file to be used, see: T92464

Reviewed by: mont29

Ref D13126

source/blender/python/intern/bpy_rna_context.h

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup pythonintern
+ */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern PyMethodDef BPY_rna_context_temp_override_method_def;
+
+#ifdef __cplusplus
+}
+#endif