Allocator: simplify using guarded allocator in C++ code

Using the `MEM_*` API from C++ code was a bit annoying:
* When converting C to C++ code, one often has to add a type cast on
  returned `void *`. That leads to having the same type name three times
  in the same line. This patch reduces the amount to two and removes the
  `sizeof(...)` from the line.
* The existing alternative of using `OBJECT_GUARDED_NEW` looks a out
  of place compared to other allocation methods. Sometimes
  `MEM_CXX_CLASS_ALLOC_FUNCS` can be used when structs are defined
  in C++ code. It doesn't look great but it's definitely better. The downside
  is that it makes the name of the allocation less useful. That's because
  the same name is used for all allocations of a type, independend of
  where it is allocated.

This patch introduces three new functions: `MEM_new`, `MEM_cnew` and
`MEM_delete`. These cover the majority of use cases (array allocation is
not covered).

The `OBJECT_GUARDED_*` macros are removed because they are not
needed anymore.

Differential Revision: https://developer.blender.org/D13502

source/blender/blenlib/intern/task_scheduler.cc

@@ -50,8 +50,8 @@ void BLI_task_scheduler_init()
   if (num_threads_override > 0) {
     /* Override number of threads. This settings is used within the lifetime
      * of tbb::global_control, so we allocate it on the heap. */
-    task_scheduler_global_control = OBJECT_GUARDED_NEW(
-        tbb::global_control, tbb::global_control::max_allowed_parallelism, num_threads_override);
+    task_scheduler_global_control = MEM_new<tbb::global_control>(
+        __func__, tbb::global_control::max_allowed_parallelism, num_threads_override);
     task_scheduler_num_threads = num_threads_override;
   }
   else {
@@ -69,7 +69,7 @@ void BLI_task_scheduler_init()
 void BLI_task_scheduler_exit()
 {
 #ifdef WITH_TBB_GLOBAL_CONTROL
-  OBJECT_GUARDED_DELETE(task_scheduler_global_control, tbb::global_control);
+  MEM_delete(task_scheduler_global_control);
 #endif
 }