finalize terminal disablePersistence API

[meganrogge]

This PR fixes #118726

[Tyriar]

Think we'll need to bring it up in the API sync but this looks like what I'd expect

[jrieken]

I am surprised myself but we actually haven't used the disable-prefix yet. That makes me wonder if can find an antonym of "persistence" which we use by itself or with the is-prefix, like transient?: boolean isTransient?: boolean (transient has been used for notebooks). The default would still be persisted terminals

[Tyriar]

That would mean we use a different word for the feature only in the api though?

[jrieken]

Sure - I'd say that's the norm and not an exception... Settings, command ids etc are kinda API but don't go by any rules. And these names also must not always aline

[meganrogge]

@jrieken should we discuss the name at the next API sync or is this good to merge?

[Tyriar]

I see we use persistent in EnvironmentVariableCollection, but it's a value given to the extension and optional booleans in the case of this API feel wrong weird when they default to false and I don't think we do this anywhere.

isTransient seems fine to me if we can't use persistent/persistence, there's always the docs to clarify.

[jrieken]

Yeah, we will probably do a quick mention at the next API sync. Tho, I don't expect this to be controversial or anyone of you to be there to "defend" it.

[andyleejordan]

Thanks so much @meganrogge!!! This will really improve the user experience for a lot of extensions.