[SAoC 2022] Replace druntime Hooks with Templates: Milestone 1, Week 4

[Jack Applegame]

On Monday, 17 October 2022 at 20:50:00 UTC, Teodor Dutu wrote:
> Hi,
>
> This week I finished lowering `CatExp`s to `_d_arraycatnTX` and 
> created [this](https://github.com/dlang/dmd/pull/14550) PR for 
> it. I still have a few small yet annoying errors to fix, 
> regarding mangling and a failure to build phobos that I cannot 
> reproduce locally. I'll work with my mentors to try to solve 
> these bugs, as they seem rather small and they probably don't 
> require many changes to the PR.
>
> In addition, I made further progress with `_d_newitem{T,iT,U}`. 
> I am looking to finish translating those hooks to a template 
> (`_d_newitemU`) by the end of this week.
>
> Thanks,
> Teodor

This is one of the most important tasks. Thank you very much.