[libomptarget] Add support for target update non-contiguous

This patch is the runtime support for https://reviews.llvm.org/D84192.

In order not to modify the tgt_target_data_update information but still be
able to pass the extra information for non-contiguous map item (offset,
count, and stride for each dimension), this patch overload arg when
the maptype is set as OMP_TGT_MAPTYPE_DESCRIPTOR. The origin arg is for
passing the pointer information, however, the overloaded arg is an
array of descriptor_dim:

```
struct descriptor_dim {
  int64_t offset;
  int64_t count;
  int64_t stride
};
```

and the array size is the dimension size. In addition, since we
have count and stride information in descriptor_dim, we can replace/overload the
arg_size parameter by using dimension size.

Reviewed By: grokos

Differential Revision: https://reviews.llvm.org/D82245