Blender Git Loki

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