Support empty data in async algorithms

[SergeyKopienko]

In this PR we implement empty source data support in async algorithms. For note: they are implemented as experimental for hetero policy only.

The goal: to align oneDPL async algorithms with sync algorithms which are able to process empty source data without assertions and so far and so on.

Algorithms list (from namespace oneapi::dpl::experimental):

• copy_async
• exclusive_scan_async
• fill_async
• for_each_async
• inclusive_scan_async
• reduce_async
• sort_async
• transform_async
• transform_exclusive_scan_async
• transform_inclusive_scan_async
• transform_reduce_async

Patterns list:

• __pattern_walk1_async
• __pattern_walk2_async
• __pattern_walk3_async
• __pattern_transform_reduce_async
• __pattern_transform_scan_base_async

Attention: please use option Hide whitespace to see diffs in this PR.