Not enough space for completion panes in multiline statements

[kindermannhubert]

We print new lines after prompt submission so we have enough space for completion panes in next input. That's ok but it's not enough for multiline inputs. See:

Perhaps we need to move the start location of completion panes from "current line" to "input start line". That would be necessary only when there's not enough space for panes. VS solves this in a similar way.

[kindermannhubert]

Also on the last few lines of code area completions are disabled (because there is no space for them). This restriction should be lifted with this enhancement.