More async support (unique_copy, upper_bound, adjacent_difference)

[beomki-yeo]

I have been working on SYCL implementation in acts-project/traccc#462 where I used some onedpl functions

I particularly need the asynchronous operations for the following functions, which seem not to be defined in asybc_extension_defs.h:

oneapi::dpl::unique_copy
oneapi::dpl::upper_bound
oneapi::dpl::adjacent_difference

Please let me know if they are defined in somewhere else already.
If not, Is there any plan to support this in the near future?