JLine 3: resolve status of `history` and `h?` commands

[SethTisue]

commented-out code in the PR:

    // TODO maybe just drop these commands, as jline subsumes them -- before reenabling, finish scala.tools.nsc.interpreter.jline.HistoryAdaptor
     //historyCommand,
     //cmd("h?", "<string>", "search the history", searchHistory),

[lrytz]

@dwijnand notes that jshell has an edit command that actually works reliably and is useful. though it's more relevant in java given it's verbosity. our edit works or not if you're lukcy.

[SethTisue]

control-R already works for searching history. (this was true in JLine 2 as well.)

[dwijnand]

Details: in jshell /edit works with my settings of EDITOR=vim while with scala I need to set EDITOR=mvim to have something that works.

[hvesalai]

emacs-sbt-mode uses the history commands as well and also expects the commands run from emacs to be there (i.e. when jline is off, I guess)

[SethTisue]

I've made this ticket history-only, labeled it a blocker, and moved the edit stuff to a new ticket (#700)

[SethTisue]

now that I take a second, slower look at this I see that :history shows the history (optional numeric argument of how many entries to show) and :h? is for searching it:

scala 2.13.1> 2 + 2
res0: Int = 4

scala 2.13.1> 3 + 4
res1: Int = 7

scala 2.13.1> 5 + 6
res2: Int = 11

scala 2.13.1> :history
  1  2 + 2
  2  3 + 4
  3  5 + 6
  4  :history

scala 2.13.1> :h? 5
3 5 + 6
5 :h? 5

scala 2.13.1> :history 2
  5  :h? 5
  6  :history 2

[SethTisue]

@hvesalai I see that emacs-sbt-mode reads ~/.scala_history; note that we're changing it to ~/.scala_history_jline3

you write "uses the history commands as well" and I'm puzzled about that. I'm looking in the sbt-emacs-mode source code and I see that it uses :completions, but I do not see that it uses either :history or :h?

based on my observations, I'm removing the "blocker" label from this, but I can add it back if you can confirm that it's specifically :history and/or :h? that you want/need

[SethTisue]

Another thing I hadn't understood before: in JLine 3, history search is connected to up-arrow. So if you type e.g. pr and then hit up arrow, it starts cycling through previous entries that begin with pr. Dotty and Ammonite both support this. It doesn't make :h? useless, I guess, but the need for it to exist is now less.

It already works in our PR, too. (Perhaps not perfectly?)