Use ui_busy_start()/ui_busy_stop() when search

[Shougo]

Fix #25980

I have removed gotocmdline() when search.
It resolves #25980 problem, but the side effect may exist.

I use ui_busy_start() and ui_busy_stop() instead.

[Shougo]

Hm.... Vim has same feature but why it is not reproduced in Vim?

https://github.com/vim/vim/blob/7002c055d560ae0b3bb1e24ad409390a5443daad/src/search.c#L1567

[Shougo]

I think the cursor is hidden when search in Vim.

cursor_on() and cursor_off() are implemented in Vim. But neovim is not.

[Shougo]

It does not resolve the original problem.

Because other cursor movements are exists like this.

I think neovim needs cursor_on() and cursor_off() like API.

[Shougo]

OK. This fix is better.