REPL autocomplete class names in empty package (current directory)

[som-snytt]

Repl doesn't currently offer autocomplete of class names in the empty package.

It's usual to have a quickie class to test in REPL. Packages are a nuisance, and also the script runner still gags on them.

Classes in packages in the current directory autocomplete fine.

How did we ever get any work done without that feature?

[som-snytt]

This depends on how the broken empty package is fixed in #10927

When I'm working in REPL, it's the moral equivalent to me of working in the empty package, though that illusion is belied by the current implementation.