Filter jetpack_search_should_handle_query does not let any WP_Query query using ES

#### tl;dr: with the current code, `jetpack_search_should_handle_query` does not let any WP_Query using ES.

This is the place where [jetpack_search_should_handle_query](https://developer.jetpack.com/hooks/jetpack_search_should_handle_query/) is applied

https://github.com/Automattic/jetpack/blob/bb884c04b32a57e3053f14c56e2f4e0138aef185/modules/search/class.jetpack-search.php#L455-L459

Right after the filter, we call the do_search() method and in the first lines of this method we just allow the main search query to run:

https://github.com/Automattic/jetpack/blob/bb884c04b32a57e3053f14c56e2f4e0138aef185/modules/search/class.jetpack-search.php#L502-L506

### My suggestion:

I think we need to remove the conditional in do_search().

Start in modules/search/class.jetpack-search.php at the linked filter application and the first lines of do_search(). Trace how the filter result reaches do_search(), then verify that non-main WP_Query instances using Elasticsearch are handled as intended; done means the conditional no longer blocks those queries and the relevant search behavior is covered.

Written by the indexing model from the issue text.