__rvalue and Move Semantics first draft

[Richard (Rikki) Andrew Cattermole]

On 09/11/2024 10:33 PM, Walter Bright wrote:
> https://github.com/WalterBright/documents/ 
> blob/5dbf6728d7d0ae46a411c720ec41e3603310172b/rvalue.md
> 
> I gave up on the previous move DIP. This one is better.

This is a restatement of what I said yesterday at the monthly meeting.

I am significantly happier with this design however:

1. We'll need to introduce a swap builtin, since we have no way to say 
describe moves between parameters. This can come later, as it is an 
addition.
2. I have the concern that existing code that is not designed to accept 
a move, will have a move into it. White listing via an attribute 
``@move`` to say that this constructor/opAssign is designed to handle a 
move in would be valuable.
3. Optimizing of eliding of destructors should be done with type state 
analysis, it does not need its own dedicated DFA.