Get rid of `BOOST_COMPUTE_ADAPT_STRUCT` integrating boost::pfr

https://github.com/boostorg/pfr

Boost PFR - it's a small library that provides basic reflection for user defined types without any boilerplated macro. Now the library have everything required from Boost Compute library (including reflection of field names) and might be integrated in order to get rid of BOOST_COMPUTE_ADAPT_STRUCT macro.

Don't hesitate to ask any question regarding PFR, my pleasure to provide as much help with development as it required.