If we switch the bind mode, we add a "force-repaint" there just to
redraw the mode indicator.
That's quite wasteful and annoying, considering that sometimes the prompt can take
half a second.
So we add a "repaint-mode" function that just reexecutes the
mode-prompt and uses the cached values for the others.
Fixes#5783.
* Add "expand-abbr" bind function
This can be used to explictly allow expanding abbreviations.
* Make expanding abbr explicit
NOTE: This accepts them for space only, we currently also do it for \n
and \r.
* Remove now dead code
We no longer trigger an abbr implicitly, so we can remove the code
that does it.
* Fix comment
[ci skip]
