bug#39512: 28.0.50; Add command isearch-yank-region

[Juri Linkov]

> Now I am using swiper which has an improved version for thing-at-point
> (something like `thing-at-point-or-region` called `ivy-thing-at-point`)
> which actually is much more useful and avoids an extra binding.
>
> https://github.com/abo-abo/swiper/blob/c6b60d34ac37bf4d91a25f16d22e528f85e06938/ivy.el#L426
>
> Implementing something like that in vanilla is (in my opinion) the best
> default behaviors for isearch-forward-symbol-at-point. But I don't want
> to go in that discussion in the mailing list because it is difficult to
> get an agreement what touching old commands. But you are free to do it
> if you want.

Indeed there are two ways to add it: as a new command (that requires a new
keybinding) or a new option (disabled by default) for the existing command.
Maybe we could enable it by default, but I don't know how it will affect
the use cases of users - maybe someone users use isearch to extend the
active region to the next matching symbol, and don't want 'M-s .' to yank
the region.