Move code to C++20

[teusbenschop]

The code base now gets compiled for C++17.

Bump the compilers to C++20.

Test it on every port.

• Android
• Linux
• Windows
• macOS
• Cloud
• iOS

Upgrade the code base to use more C++20 features.

[teusbenschop]

The compilers of all port compile with language dialect C++20.