Support hiding flags/subcommands/possible values/aliases for native compeletions

[epage]

We shouldn't offer hidden options by default but complete them if the user starts typing them

See #3166 for more details on native completions

• code
• tests

[shannmu]

i will work on this later.

[epage]

Before we do this:

• We should make sure subcommand visible aliases are supported

In doing this, we should hide hidden items by default unless there are no other completions available.

[epage]

PR #5283 started work on this but it seemed to have stalled out

Per usual, I would like to see

• Tests added / updated in one commit, showing current behavior
• As features are implemented, update the tests so they show the new behavior and the diff shows the change in behavior

see also my comment from that PR:

There is one point I wasn't clear about in the expectations for this: we should probably keep a completion hidden unless there are no visible choices.

In reviewing this, I also noticed

• I didn't mention hidden aliases

• We aren't showing visible subcommand aliases

I do find it less than ideal how inconsistent we are with where we check is_hide_set. However, I assume cleaning that up would naturally fall out of the above as we'd need to start returning (value, is_hidden, help) (maybe turned into a struct? if so, ideally that refactor would be its own commit) so we can handle all of these cases.