fixes #16052 MultiSelect and Listbox filterby is not working

[ymg2006]

#16052 MultiSelect and Listbox filterby is not working
This commit synchronizes the get searchFields(). Seems it is update in other places except these two components.

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Name	Status	Preview	Comments	Updated (UTC)
primeng	⬜️ Ignored (Inspect)	Visit Preview		Jul 18, 2024 0:37am

[rosenthalj]

I believe that this PR #16052 may break the following modification to the PrimeNG "basic" demo example (replacing all City interface references to string) :

<div class="card flex justify-content-center">
    <p-multiSelect 
        [options]="cities" 
        [(ngModel)]="selectedCities" 
        placeholder="Select Cities" />
</div>

export class MultiSelectBasicDemo implements OnInit {

    cities!: string[];

    selectedCities!: string[];

    ngOnInit() {
        this.cities = [
            'New York',
            'Rome',
            'London',
            'Istanbul',
            'Paris'
        ];
    }
}

Note: Testing your changes against all the the PrimeNG multiselect demos would not have been"complete" since all the demos define optionLabel.

[mertsincan]

For now, closed! If a new update comes from your side, please reopen this PR. Thanks a lot for your understanding!