Add displayValues option to respect property order

[jimsafley]

See #2391. Adds "propertiesRespectOrder" option to AbstractResourceEntityRepresentation::displayValues(). Setting it to true changes default behavior to respect the order of properties passed in the "properties" option. The default behavior is to maintain the original property order, irrespective of the passed order. For example, this:

$item->displayValues(['properties' => ['dcterms:subject', 'dcterms:description', 'dcterms:title']]);

will, in most cases, output "Title, Description, Subject" because that's the order defined on the resource itself. Whereas, this:

$item->displayValues(['properties' => ['dcterms:subject', 'dcterms:description', 'dcterms:title'], 'propertiesRespectOrder' => true])

will output "Subject, Description, Title" because "propertiesRespectOrder" is true, and that's the order passed in the "properties" option.

[zerocrates]

This won't work properly if properties contains terms that the resource has no values for: you'll get an entry for the "missing" terms in the final result when you shouldn't (despite its name, array_replace will introduce new keys in the result that aren't in the first arg).

It's possible to fix this with more array_ calls... one option that comes to mind would be doing another array_intersect_keys with the original $values passed second to drop out anything in we don't actually have a value for... but we may just want to swap this out with a foreach:

$result = [];
foreach ($options['properties'] as $term) {
    if (isset($values[$term])) {
        $result[$term] = $values[$term];
    }
}
$values = $result;

[jimsafley]

I feel that propertiesRespectOrder is an awkward option name. It implies that the default behavior is somehow not respecting an order. Maybe a better option is originalOrder with the default set to true? That way the default behavior remains the same, and originalOrder=false respects the order passed in properties.

[zerocrates]

I'd want properties first in any option as this is something that only works with the properties option. propertiesOrdered or whatever if we want to shorten it, i'm fine with. The reverses, like propertiesOriginalOrder also fine, but also kind of long.