Replace -> with :: where appropriate in docstrings (#57012)
In cases where a function is documented as
```
function(arg::ArgT, arg2::Arg2T) -> RetT
...
```
I either switched ` -> ` to `::` or switched `RetT` to `ret_name::RetT`.
From the recommendation and justification from @nsajko here:
https://github.com/JuliaLang/julia/pull/56978#discussion_r1909183080 and
applied throughout the repo.
As documented here #57583
Also includes some minor changes to touched lines (e.g. removing annotations that are just clutter)
