Vim command mode autocompletion selection state is sticky between typing bursts

[Samonitari]

I report a vim command mode autocompletion issue again 💌

Issue title says it mostly. Selecting an autocompletion suggestion causes some misbehaviour - I think.
User can't consistently select the first suggestion with one key!

Here are two real life scenarios that have confusingly - or dare I say frustratingly - different results:

Scenario 1:

• type :chdir ~/Do -> suggestions kick in, with the current user's "Documents" as the first option (assuming English OS setup)
  no suggestion is selected now
• press Tab or Down -> command gets completed with the first suggestion

Scenario 2:

• type :chd
• press Tab or Down -> autocompletion filled to "chdir" command
• type ~/Do -> suggestions kick in, with first suggestion selected
• press Tab or Down -> command gets completed with the second suggestion

Scenario 2 can be reproduces by multiple 'tabbing' in only the path also - you don't need the first tab in the command of course.
Thanks to @CrossR for the help in Discord, he found the offending lines here

[CrossR]

My assumption here is that (at least for the vim command line), we don't want the behaviour in the linked code, as persisting the currently focused item doesn't mean anything here, since its basically a fully new set of items.

I'm guessing that code is useful for cases where data is streaming in?

So perhaps it needs an additional parameter or some way of distinguishing between "yes this is an update" and this which is less of an update and more of a full new set of items. Perhaps a new action then, that sets the full set of items as you could argue this isn't really "UpdateFilterProgress" and actually something else.