The objective is to add support for Public API SortClause objects input parsing for REST.

It may have synergies with the recent implementation of Fields in Views filters (EZP-28783).

Input format

Support for the following should be added to `ViewInput` version 1.1:

<ViewInput>
  <LocationQuery>
    <SortClauses>
      <Field contentTypeIdentifier="article" fieldDefinitionIdentifier="score">ascending</Field>
      <!-- alternative, friendly syntax -->
      <Field identifier="folder/comments_count">descending</Field>
    </SortClauses>
  </LocationQuery>
</ViewInput>

The JSON version will derive from that.

Error handling

Error handling should rely on the execution of the Query, like content/views does right now.