replace `@pure` annotations in Base with effect settings (#44776)
This commit replaces `@pure`/`@_pure_meta` annotations used in `Base`
with corresponding effect settings (`:total` or `:total_or_throw`).
The concrete evaluation mechanism based on the effect system (#43852)
has the following benefits over the `@pure`-based optimization:
- it can fold cases when consistent exception is thrown
- it can handle constant union-split situation as well
- effects can be propagated inter-procedurally
While revisiting the existing annotations, I removed some unnecessary ones
and also added some more hopefully new annotations (mostly for reflection utilities).
In theory this should give us some performance benefits, e.g. now we
can concrete-evaluate union-spit `typeintersect`:
```julia
@test Base.return_types((Union{Int,Nothing},)) do x
typeintersect(String, typeof(x))
end |> only === Type{Union{}}
```
Though this commit ends up bigger than I expected -- we should carefully
check a benchmark result so that it doesn't come with any regressions.
