Support repl_ast_transforms

[knuesel]

This is to discuss the possible re-inclusion of repl_ast_transforms support (originally added in #947 but reverted because of a bad interaction with Revise). Could it maybe be added back as an opt-in feature?

My use case is to get https://github.com/rfourquet/SafeREPL.jl working in some notebooks.

[JamesWrigley]

Hmm so this is how Revise hooks into the REPL. Turns out it basically does the same thing as the new hook in the Revise extension 🙃 https://github.com/timholy/Revise.jl/blob/9e5262ac548aff13c8f99b64820e5549405d1b01/src/packagedef.jl#L1277