identify traits in libstd that should use associated lifetimes

[pnkfelix]

as a subtask of #17307, once the associated lifetimes part of associated items is implemented, we will want to update libstd to use it.

My google doc from #17826 includes a column for associated lifetimes; I copied the link again below.

Most/all of the cases are related to slice traits, and its possible that they will just go away with other design changes. I am not sure.

https://docs.google.com/spreadsheets/d/1Y_NAgzEK3FWcG0LjcykyKJEAibSFI3w-v-ekZ4GU8n4/edit?usp=sharing

[pnkfelix]

Nominating.

I had thought this would not block 1.0, but @aturon points out here that we do not intend for lifetimes to be used as "input" parameters on a trait, but we still need to associate them and refer to them.

So this is probably P-backcompat-libs. And depending on what libraries are affected, it may also be on the 1.0 milestone.

[aturon]

@pnkfelix I added a comment to the subtask for implementing associated lifetimes to clarify how I see things.

[pnkfelix]

Assigning P-high, not 1.0 milestone.

[aturon]

Closing; due to DST, no traits in std actually need this.