Warn about using the GC

[Richard (Rikki) Andrew Cattermole]

On 15/01/2024 1:21 AM, claptrap wrote:
> Nobody who uses @nogc is complaining about it. The people who are 
> complaining are people who don't use it, they are complaining because it 
> puts extra burden on them to support it. Or it's causing fragmentation. 
> (Thats my impression anyway)

I have over 100k LOC annotated with ``@nogc``. That is also -betterC.

I am complaining.

I also want contract invalidation to help make the transition for 
callbacks much more seemless to remove the perceived fragmentation.