[code-quality] [jcalendar] remove jcalendar usage from participant_register_date on event search

[eileenmcnaughton]

Overview

This removes one more place where legacy jcalendar is used.

Before

Deprecated pattern used

After

preferred pattern used

Technical Details

There is actually still one left on the form (event date)
which I left out for now as it involves thinking about the fact event is a different entity & might warrant different representation in the arrays

Comments

@seamuslee001 @mattwire @colemanw maybe one last push will rid us of that pesky jcalendar....

[civibot]

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[seamuslee001]

not having much luck with jenkins @eileenmcnaughton https://test.civicrm.org/job/CiviCRM-Core-PR/26418/checkstyleResult/new/

[eileenmcnaughton]

@seamuslee001 sigh - and I'm the one that wants to make it stricter!

[eileenmcnaughton]

@seamuslee001 @mattwire @colemanw so I think when converting these fields there are a few gotchas ./ things to check

1. does a smart groups still work if it has been upgraded
2. do the dates stay relative - in the brave new world the saved form values should look like

         [participant_register_date_relative] => this.month
                            [participant_register_date_low] => 
                            [participant_register_date_high] => 

But without this hack it was saving the resolved date - which we would expect to create issues like https://lab.civicrm.org/dev/core/issues/389

I would ideally like to get this one merged before the next rc is cut

[eileenmcnaughton]

test this please

[mattwire]

Tested and works here