WithIOContext: properties of the original IO should not be hidden

[fonsp]

See the compat entry in the changed files.

This could technically be breaking, but I doubt that anyone relied on the original IO context being hidden.

Example

Here, the :displaysize and :limit from Pluto's display are being hidden:

After this PR, the matrix gets rendered properly:

[github-actions[bot]]

Try this Pull Request!

Open Julia and type:

  julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/JuliaPluto/PlutoUI.jl", rev="WithIOContext-layer")
julia> using PlutoUI

Or run this code in your browser: