Exercise `FieldExtractPreference.EXTRACT_SPATIAL_BOUNDS` in ES|QL block loader tests

[lkts]

#125164 and PRs before have added a new set of tests that specifically target block loaders (see #115257).

Specifically #125164 added GeoShapeFieldBlockLoaderTests and ShapeFieldBlockLoaderTests but these tests don't cover custom logic related to FieldExtractPreference.EXTRACT_SPATIAL_BOUNDS. They should be extended to cover it. Currently this behavior is tested only by CSV tests.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)