Discuss upgrade to c++20

Description

With C++20 being technically finalized all that remains is the standard publication and hence we are save to use features of c++20 already supported by the compilers we employ. The support improved significantly with the publication of clang10 and the recently released gcc10. A list of currently supported c++20 language and library features can be found here.

Proposal

Discuss in this issue if we already should switch to c++20, in light of the currently limited list of available features, as started in #190 (closed).

Related issues

Meta-task: #190 (closed)