SearchKit - Add pseudo-fields for row number and current user

[colemanw]

Overview

Makes a couple calculated fields available for use as columns or tokens in SearchKit.

Before

No option to display current user or row number in columns or tokens

After

New columns available:

New fields also work as tokens:

[civibot]

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[eileenmcnaughton]

Generally works but I noted
(on demo now )
http://core-21435-8bdvx.test-1.civicrm.org:8001/civicrm/search#/display/contacts/dd

1. you can try to sort the by the pseudofield columsn - but you can't succeed

2. in search form you can click on page 3 & row number will say 110 - but in search display & afform it will say 10

3. if you export then the row number re-numbers from 1 (that might be by design - not sure)

[colemanw]

@eileenmcnaughton I have pushed up a fix to the first problem.
The second was actually a regression and I fixed it in #21488 - it wasn't just the count that was displaying incorrectly on subsequent pages, it was everything.
The third I think we can safely ignore for now.

[eileenmcnaughton]

ok - that seems to be working now