Allow users to directly mention files in the prompt (instead of using def())

[bzorn]

Since we allow a prompt to say "write to file foo.md", it would be a parallel capability to be able to say in the script prompt:

"The important information you need is in file foo.md. Read that file and answer these questions..."

Versus having to say:

def("INFO", env.files, ...)

[pelikhan]

We could support the @uri syntax of copilot chat.