stdexec and P3109

[laramiel]

Hello-

Based on P3109, there are a few pending changes to std::execution. The most invasive change appears to be removal of tag_invoke. Is there a branch where this work is/will take place?

[ericniebler]

The paper proposing to replace tag_invoke is P2855, the most up-to-date version o which can be found here: https://isocpp.org/files/papers/D2855R1.html

Ville's implementation is a work in progress. It lives here:
https://github.com/villevoutilainen/wg21_p2300_std_execution/tree/P2855_member_customization_points