stage2: make repl ui better

[g-w1]

As stage2 is improving, I found myself using this repl more and more and it was annoying to type out update every time, so I updated the ui.
"" runs the previous command
Any first letter for a command also works for the command itself. As we add more commands, this could be fleshed out more to avoid collisions.
I made it print updating... every time so that if you did "" and it took a short time 🥳 you would know it was actually updating and not just skipping. Should a different message print here?

[andrewrk]

I made it print updating... every time so that if you did "" and it took a short time partying_face you would know it was actually updating and not just skipping. Should a different message print here?

It should print nothing because we already have the progress bar that shows up after 0.5 seconds!

However if we want to indicate that an update occurred, we could have it print something more useful such as:

Update completed; 3/100 files changed, 123/900 decls modified, 12 added, 34 deleted

or something to that effect.

[g-w1]

Thanks, this is just the kind of feedback I was looking for!

[g-w1]

I found finding added/deleted decls hard, but I think this is good enough for now:

[g-w1]

Ok, finally got around to making it show how many were added or removed thanks to help from andrewrk on irc.

[g-w1]

I will rebase soon as #8554 was merged and included a lot of the same kinds of stuff.

[g-w1]

Closing as actually the features that I most wanted were added.