[Maps] Spatial Join UI updates

[mdefazio]

As a follow-up to #156618, I wanted to throw out some thoughts on how to minimize the panel overlays that currently happen within the UI.

The spatial join UI uses the Expression format and opens a popover. Due to the complexity of options, it can quickly get into a scenario where several popovers are overlapping.

While I know there is more thinking involved around this, it may be worthwhile to consider shifting towards a similar pattern used in Lens and open a new full height panel/flyout. This will help the user keep context and focus on one set of UI's at a time.

Imagine the below Lens example, but rather than Breakdown, it showed Spatial Join (or Term Join), with the option to add additional ones below it. Clicking on this title would then open the second screenshot where we can house more of the join options/settings in a dedicated view.

Again, I acknowledge there is more needed here as this explanation is quite abstract. However, I wanted to drop this in an issue in case we wanted to explore some more options for the UI and potentially reuse some existing patterns.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[ThomThomson]

Closing this and adding it to the maps icebox.