Support IJulia in `artifact_str` (#60877)
IJulia evaluates cells with the source file set to e.g. `In[3]`.
`artifact_str` only supports the REPL prefix so calling `artifact"foo"`
in a notebook would fail. Also fixed a wee typo in the docstring.
Disclaimer: I'm not sure this is the best way to fix it. Hardcoding
support for an external package (even one as important as IJulia) into a
stdlib feels a bit wack. But I'm also not aware of any API to get the
prefix, and I don't know of any other package that needs such support.
Fixes https://github.com/JuliaLang/IJulia.jl/issues/1060.
