Line numbers inside secondary prompt

[snuyanzin]

While editing of long queries it would be good to see line numbers with ability to switch on/off permanently like via properties and while editing like widgets

here it is a short demo showing my current version without docs update (snuyanzin@db9e102) for that
https://asciinema.org/a/257103?speed=2.5 (by the way it looks like asciinema bug: if try to change number of cols/rows via url then in the second part of the video the lines started to be broken).

There is at list one minor thing which is impossible to fix without changes in jline3 - it could pad only by one char not by string. More details are in jline/jline3#375 (comment)

[julianhyde]

Wow!

[snuyanzin]

Merged as 9d3bb0b

Also added alt-ctrl-n into docs in key-stroke section