fix(updateSelectizeInput): Clear current value before update if selected and sever = TRUE

[gadenbuie]

When a user calls updateSelectizeInput() with server = TRUE and they provide both new choices (required by server = TRUE) and a new selected value, the current value of the select input may not be part of choices. When the old value isn't in choices, those options will remain in the select options after the options are updated.

This PR updates the client-side JS for a server = TRUE update to clear the current select input value when selected is provided, to avoid the persistence of the old values in the select options.

When selected is not provided, we'll still run into the previous behavior, but I don't know if there's anything we can do about that since the client doesn't have complete information about the set of choices.

Fixes #3966

[cpsievert]

Just noting that .clearOptions() did in fact intentionally make this change (of not .clear()-ing the selection) in v0.15.2:

selectize/selectize.js@5b15d3b
selectize/selectize.js#1079

However, the docs didn't get updated to reflect this 😞

https://selectize.dev/docs/API/selectize#clearoptionssilent

[cpsievert]

Nice catch and fix, thanks!