SearchKit - Fix display of links in aggregated columns

[colemanw]

Overview

Fixes an error caused by trying to make an aggregated column into a link.

Before

• Create search for Activities
• Add LEFT join for Activity Contacts
• Run search, notice that contact display name column is not shown as links
• Create a display, notice that configuring the contact display name column as links will cause an error

After

Same as above, links work correctly. Also prevents you from adding links when using any aggregate function other than GROUP_CONCAT since it's the only one that can show each aggregated item individually.

Technical Details

This gives special treatment to the GROUP_CONCAT function in SearchKit to match the special treatment it gets in APIv4 (exploding it into an array).

[civibot]

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[eileenmcnaughton]

@kurund were you going to test & hopefully merge this one too?

[kurund]

@colemanw @eileenmcnaughton

I have tested and is working as expected. Good to merge.