Changed docs for redirect functions to reflect what types they handle

[thomasyang1207]

Pipe is not a subclass of IOStream or LibUVStream, but is a subclass of AbstractPipe, which the redirect family of functions does not currently handle.

[kshyatt]

This addresses #31145. @thomasyang1207 (welcome to Julia!) was maybe interested in getting these methods to work for Pipes again if anyone wanted to provide some guidance!

[JeffBezanson]

Pipe endpoints and IOStreams (usually a file opened by open) are also supported. You can pass a pipe endpoint using e.g. pipe.in, but I'm not sure if that's recommended.

[tlienart]

Shouldn't this currently just be Union{Base.LibuvStream, IOStream} as per https://github.com/JuliaLang/julia/blob/master/base/stream.jl#L1024 ? (I guess that's what Jeff is pointing out before)

Also maybe it would be nice to add an example? for instance with IOStream:

foo() = println("hello");
open("test.test","w") do outf
    redirect_stdout(outf) do
        foo()
    end
end

(PS: apologies if I'm polluting this PR, I saw the issue #31145, started replying there and then realised this PR was still open)

[vtjnash]

Yeah, let's just make Pipe work

[StefanKarpinski]

Can you open an issue for making Pipe work then?