[REF][PHP8.2] Convert dynamic property into a variable

[braders]

Overview

Convert dynamic property _softIndividualId into a variable, as the value is only used within a single function.

Before

Use of dynamic property is deprecated in PHP 8.2.

After

Dynamic property is no longer used, a variable is used instead.

[civibot]

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[colemanw]

I have to say, these old dynamic properties were quite troublesome. I think most of the time they were done that way out of loyalty to an established pattern (as if $this->_foo were somehow better than $foo) but they only served to confuse future devs trying to figure out if the variable could be removed or if it was secretly used from some other place that required it to be part of the class. Thanks for doing that detective work.