[APP-4532] - Replace <SearchableSelect> with svelte-select

[micheal-parks]

Overview

This PR replaces our <SearchableSelect> component with the svelte-select library. I did plenty of restructuring here to try to ameliorate the UX confusion and architectural problems that have arisen out of this component.

Changelog

• Replace <SearchableSelect> with svelte-select
• Rename <SearchableSelect> as <AutocompleteInput>. The original name is confusing and led to the problematic exclusive prop.
• Remove exclusive prop. This added unnecessary complexity - areas of app that use this should just use a <Select> component.
• Split out multiple prop into <Multiselect> component. This prop was overloading the behavior of this component.
• replace the cx prop in favor of class. I would like us to move toward this pattern for all prime components. Adding a cx prop introduces an unnecessary dependency considering any part of app can import cx and pass the resulting string to a Prime component. This also follows the general pattern of "spread whatever you can into the underlying element whenever possible". proposing this later to move this through and avoid delays based on discussion

Next steps

I'll immediately bump app and fix all breaking changes. I've scanned through what's needed - it won't be too bad.

• Todos in app about adding a required field can be removed, svelte-select supports the required prop.

[mcous]

Quick initial thoughts. Very excited for this

[mcous]

thought (performance): This might be less of a big deal once Svelte 5 is in play, but this list of objects situation has given us a lot of grief in terms of unnecessary DOM operations from this component. I wonder if there's a path here - maybe in a future PR - where we lean more heavily into slots / snippets for stuff like option metadata rather than try to jam it all into props. Seems a little closer to how svelte-select itself works