feat(corfu): general move-to-minibuffer impl

We previously implemented only consult/vertico as a target for export,
now we have all of them. It was necessary to use case-by-case
conditions, unfortunately, because other UIs have subtle quirks that
prevent a single generalized approach to work.

Ivy is almost compliant, but it needs beg and end to not be markers.

Helm doesn't replace `completion-in-region-function`, it expects to go
around the default `completion--in-region`, so a small addition was made
to its module, because we weren't doing that. This was likely an
oversight due to the non-standard usage. This was fixed here because we
need it working for this feature.

Ido doesn't implement `completion-in-region` and its `completing-read`
is retricted to a list of strings as table, so it's treated the same as
absence of a framework, because it lacks the needed features.

modules/completion/corfu/config.el

@@ -32,6 +32,8 @@
         tab-always-indent (if (modulep! +tng) 'complete tab-always-indent))
   (add-to-list 'completion-category-overrides `(lsp-capf (styles ,@completion-styles)))
 
+  (add-to-list 'corfu-continue-commands #'+corfu-move-to-minibuffer)
+
   (add-hook! 'minibuffer-setup-hook
     (defun +corfu-enable-in-minibuffer ()
       "Enable Corfu in the minibuffer if `completion-at-point' is bound."