[Maps] Fit to data should take into account joins

[thomasneirynck]

Since 7.3, features without a corresponding result in the join are now hidden.

The Fit-to-data action does not take that into account, and will fit to all features.

This was intentional, because the maps app does not necessarily know if there are features outside the visible bounds that may have a corresponding result in the join. This could be the case when the source are documents from an index-pattern.

In hindsight, that behavior now seems wonky for the 80% use-case. Usually, the source layer is static, and we know the extent of all features and their left-key properties (e.g. EMS). The fit-2-data should fit what's on screen in those cases. Or at least, this should be the behavior if a join is configured on the vector layer.

[elasticmachine]

Pinging @elastic/kibana-gis