Fix for issue #2805 by using company-finish on counsel-company.

[joefbkohler]

Simple change that makes counsel-company work more seamlessly with company-complete. By using company-finish instead of ivy-completion-in-region-action many behaviors expected from company, like 'keep-prefix' option and post-complete hooks now work.

This change needs that company-abort be called only if ivy-exit is nil when unwinding, otherwise company-finish does not work.

[usaoc]

Hi, a few comments here if you don't mind.

1. I don't think we still need the variable len if we are not bothering with ivy-completion-in-region-action. We also don't need to set ivy-completion-{beg,end}.

2. We could wrap the ivy-read part with (when company-candidates ...) so that it does nothing when there is no candidate, replicating the behavior of company-complete.

3. I suspect that the workaround is not needed. The problem is that we are dealing with outdated company-candidates because company-complete-common inserted the common part without updating the variables. In fact, I think we could just call company-abort and then company-complete before calling ivy-read so that the variables are properly set. It also solves the problem that the text properties of the candidates are incorrect (the completed common part is not properly propertized).

[NightMachinery]

I am also touching this, and I think my changes could be integrated into this PR:

https://github.com/abo-abo/swiper/pull/2849