Impact of C++20 deprecations on our code

C++20 deprecated the following:

1. implicit capture of this in [=] lambda capture
2. arithmetic with enums

   E1 | E2
   val * E3
   

3. some uses of volatile (basically everything except straight loads and stores)
   • already have some fixes in qvolatile_p.h
4. comma operator in [ ] subscripts (in preparation of C++23 adding multi-dimensional subscripting)

We need to fix the fallout (most of it done at this point, but we need to continuously fix issues in new code).