[release/8.0] Make src gen for property setters consistent with reflection (#92167)

[release/8.0] Make src gen for property setters consistent with reflection (#92167)

* Make src gen for property setters consistent with reflection

* Don't default value during initialization

* Remove unnecessary bang operator

* Don't default a property when it is a collection or child type

* Simply use of new variable; add to test

* Review feedback

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Co-authored-by: Steve Harter <steveharter@users.noreply.github.com>