Show REPL tab complete hints for public names only

[IanButterworth]

REPL tab complete hints should be helpful for guiding discoverability, therefore since #50105 has merged it seems logical to make hints only show for public names etc.

IIUC currently both public and private names are hinted.

Tab complete could still complete private names, but the user would need the knowledge that they exist, or just be trial-and-erroring their way through.

[brenhinkeller]

It's logical, but also feels a bit evil 😆

[fonsp]

In Pluto we currently show all fields, but private names are greyed out, and they score lower in our sorting:

Maybe the REPL could do something similar?