Add ivy-update-view

[juan-leon]

I think it could be useful to have an interactive function called
ivy-update-view that when invoked allow you to select one of your existing
views (ideally with the last view that user switched to in the top) and do the
equivalent of a ivy-push-view.

For me, for instance, it could replace the need for a "workspace manager" (like
eyebrowse). I never used any of those for more than a few hours (as they
involve too many new keybindings and/or are too opinionated), but I really like
the "ivy views" and a single keybinding could be enough for me to jump into the
idea of those.

(I would even configure projectile-switch-project-action to look for an ivy
view and switch to it if exists (else do magit-status or projectile-dired
depending on other things)

[abo-abo]

Nice idea, thanks. Please test.

[juan-leon]

Works like a charm, thanks.