Copy Constructor DIP and implementation

[RazvanN]

Hello everyone,

I have finished writing the last details of the copy constructor 
DIP[1] and also I have published the first implementation [2]. As 
I wrongfully made a PR for the DIP queue in the early stages of 
the development of the DIP, I want to announce this way that the 
DIP is ready for the draft review now. Those who are familiar 
with the compiler, please take a look at the implementation and 
help me improve it!

Thanks,
RazvanN

[1] https://github.com/dlang/DIPs/pull/129
[2] https://github.com/dlang/dmd/pull/8688