Try to make Core be more modern per c++20

[dhthwy]

There are definitely parts that need some refactoring, I think.

The intent was not to change any behavior or risk changing behavior, so refactoring was kept to minimum.

[dhthwy]

I tested most of this. Ought to have tests for all the commands. Manual checking sucks.

The keybinding commands work as expected with std::views::drop and std::views::reverse.

[dhthwy]

Alright, for the most part, I only did the stuff I could verify, so I guess that's it for now.

I added a couple of utility functions to miscutil.h for replacing backslashes to forward slashes. Didn't use ranges there to avoid adding another include.

[dhthwy]

I'll probably close this soon so it doesn't muddy up the PR queue. Can reopen later if there's actually a push to rewrite.

I figure there is reluctance to change known working code just for the sake of modernizing pieces of it. However, there are some parts where I think it adds some clarity and may help avoid bugs in the future for anyone that has to work on it.

Usually I inquire first before PRs like this.

[ab9rf]

I'm not ignoring this PR, I just haven't gotten to it yet. You needn't worry about messing up the PR queue.

[dhthwy]

Should've separated those commits I suppose.