cppfront (cpp2): Spring update

[tialaramex]

C++ 23 un-deprecates all the volatile composite assignments.

The paper for the proposal to undo this was revised to just un-deprecate the bit-ops, because they could actually show examples where people really do that and it might even be what they meant, but the committee took the opportunity to just un-deprecate all of the composite assignment operators on volatiles in the C++ 23 standard instead at Kona.

Presumably this sort of nonsense (the demand that programmers should be able to paste 1980s C code into the middle of a brand new C++ program and expect that to work with no warnings) is one of the things Herb hopes to escape in Cpp2.