Restrict a Note's Contact Lookup Based on the Parent Quote's Billing Account

<?php

$viewdefs['Contacts']['base']['filter']['basic']['filters'][] = array(
    'id' => 'filterContactByParentAccount',
    'name' => 'LBL_FILTER_CONTACT_BY_PARENT_ACCOUNT',
    'filter_definition' => array(
        array(
            'account_id' => ''
        ),
    ),
    'editable' => true,
    'is_template' => true,
);

<?php
//TAI-JEK-Feb. 2021-Add an initial filter to the billing_contact_name field so it only shows Contacts related to the Billing Account.
//Loop through all panels on the Quote Layout.
foreach ($viewdefs['Quotes']['base']['view']['record']['panels'] as $i => $panel) {
    //Loop through all fields on the Layout looking for the field we want to modify.
    foreach ($panel['fields'] as $j => $field) {
        if(is_array($field)){
            if(isset($field['name'])){
                $fieldName = $field['name'];
            }
        }
        else{
            $fieldName = $field;
        }
        if ($fieldName == 'billing_contact_name') {
            //Will set the custom filter here
            $viewdefs['Quotes']['base']['view']['record']['panels'][$i]['fields'][$j] =
                array (
                    'name' => 'billing_contact_name',
                    'initial_filter' => 'filterContactByParentAccount',
                    'initial_filter_label' => 'LBL_FILTER_CONTACT_BY_PARENT_ACCOUNT',
                    'filter_populate' =>
                        array (
                        ),
                    'filter_relate' =>
                        array (
                            'billing_account_id' => 'account_id',
                        ),
                );
        }
    }
}