Make any character insertion end history search

Currently, if you enter `echo` and press up-arrow, it might select
e.g. `echo foo`.

You can then enter text, making it `echo foobar` and press up-arrow
again, but the search string is *still* `echo`.

Many *other* input functions will end history search, including e.g.
expand-abbr, so pressing space by default will already end it.

So this ends the history search once you input something.

Incidentally this allows suggestions to work in this case, so it

Fixes #10287

Note that autosuggestions have been disabled while history search is
active since a08450bcb6, I'm not sure
it's actually *needed*, so it would also be possible to enable it in
that case.

But since this is already awkward (history search is *active* but with
the old search string) and I'm not sure if e.g. suggestions during
history search would be too busy, let's do this first.

src/reader.rs

@@ -1859,6 +1859,8 @@ fn readline(&mut self, nchars: Option<NonZeroUsize>) -> Option<WString> {
 
                     if elt == EditableLineTag::Commandline {
                         zelf.clear_pager();
+                        // We end history search. We could instead update the search string.
+                        zelf.history_search.reset();
                     }
                 } else {
                     // This can happen if the user presses a control char we don't recognize. No