[EuiInMemoryTable] Remove spacer after childrenBetween

[cchaos]

Closes #4246

When childrenBetween was added, it also added a conditional spacer between it and the search bar (keeping the spacer that existed before the table). The main consumer for needing teh childrenBetween doesn't want this spacer/wants to manually handle this spacing that exists between the children and the table.

This PR, moves the pre-existing spacer to only display if the search bar exists and after the search bar (before the children). So if consumers addd any childrenBetween they will need to add their own spacer between it and the table.

The only possible implications with this change is that it does now make the pre-existing spacer conditional upon the presence of the search bar. So if consumers were using the EuiInMemoryTable without search, it did have a large spacer between the content that came before it which they may have accounted for. But now that space is gone.

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I also updated one of the examples to use Facets instead of checkable cards as the more appropriate component.

Checklist

• [ ] Check against all themes for compatibility in both light and dark modes
• Checked in mobile
• [ ] Checked in Chrome, Safari, Edge, and Firefox
• [ ] Props have proper autodocs
• Added documentation
• [ ] Checked Code Sandbox works for the any docs examples
• Added or updated jest tests
• [ ] Checked for breaking changes and labeled appropriately
• [ ] Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[cchaos]

cc @pgayvallet

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_4248/

[thompsongl]

Makes sense and looks good!

+1 to the external state example updates, also