[Vega] Cancel discarded searches

[lukasolson]

When a user issues a search request in a Vega visualization, we need to cancel it in the following scenarios:

1. When the user navigates away before the search completes
2. When a new search is requested before the prior one completes

[elasticmachine]

Pinging @elastic/kibana-app-arch

[alexwizp]

@lukasolson now Vega uses new search API #68257. I think we can close this issue.

[lukasolson]

Are we properly sending the abortSignal to the search service, and properly aborting the abortController within Vega?

[alexwizp]

I hope yes, we take abortSignal from theExpression Execution Context and then pass it into search service. Is it correct?
See src/plugins/vis_type_vega/public/vega_fn.ts

[Dosant]

I checked that vega properly cancels search requests