Print fallback REPL prompt before user input (#58210)
Using the fallback REPL interactively prints the prompt only after user
input, making the scrollback confusing:
```
$ JULIA_FALLBACK_REPL=1 julia
1 + 2
julia> 3
```
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Co-authored-by: Jameson Nash <vtjnash@gmail.com>
Co-authored-by: Dilum Aluthge <dilum@aluthge.com>
