Enable future preserveSharedStateOnUnmount on instantsearch

[indykoning]

See: https://www.algolia.com/doc/guides/building-search-ui/widgets/show-and-hide-widgets/vue#enable-preservesharedstateonunmount

This feature will be default in a future release of Instantsearch.
Enabling this will prevent bugs by not removing search filters when their respective component gets removed. As long as an element still uses it.

What could happen before this addition is you setting a default value in an ais-configure element, and removing the element when a different value is passed:

<ais-state-results v-slot="{ state: { query } }">
    <div>
        <ais-configure
            v-if="!query"
            :query="query || '__NO_QUERY__'"
        />
    </div>
</ais-state-results>

<ais-search-box>
...
</ais-search-box>

If preservesharedstateonunmount is false v-if="!query" would cause ais-configure to unmount.
Forcing query to be set to null, thus re-mounting the ais-configure component and setting query again.
If preservesharedstateonunmount is true, instantsearch detects ais-search-box updates query as well. And does noet clear the querys value

[royduin]

Should we extract this somewhere? I see this (and other attributes) multiple times in different files

[royduin]

Conflicts 😇 and we need this for 4.x and 5.x?