In CMS-13433, support has been added to select an XPage layout

We now need to select the XPage layouts provided by the HST

Part 1: Repository Folder Workflow changes

In CMS-13436, support has been added for subprototypes when creating a new document via the FolderWorkflow. It was based on the folder workflow being able to added mixin or child nodes to the newly created document.

However it turns out to be too limiting : In CMS-13433 it turned out that when creating an hst:xpage below an XPage document variant, a transformation of the node structure is needed (eg hippo:identifier property must be taken and used as nodename below the hst:xpage of the document variant). Hence, simple copy-as-is in the Folder Workflow does not give us enough flexibility.

Instead, we need a more flexible approach where a downstream project to the repository can create more advanced new documents. The approach we will take is as follows: To the FolderWorkflow we add:

   /**
     * @param jcrTemplateNode the JcrTemplateNode that will instruct which mixins, properties and children to add to the newly created document
     * @see #add(String, String, String) only including an JcrTemplateNode object to add extra mixins, properties and children to
     * the newly created node
     */
    String add(String category, String type, String relPath, JcrTemplateNode jcrTemplateNode)
            throws WorkflowException, MappingException, RepositoryException, RemoteException;

  
    /**
     * @param jcrTemplateNode the JcrTemplateNode that will instruct which mixins, properties and children to add to the newly created document
     * @see #add(String, String, Map) only including an JcrTemplateNode object to add extra mixins, properties and children to
     * the newly created node
     */
    String add(String category, String type, Map<String, String> arguments, JcrTemplateNode jcrTemplateNode)
            throws WorkflowException, MappingException, RepositoryException, RemoteException;

The 'JcrTemplateNode' can contain mixins/properties to be added to the document variant AND it can have chilren. The JcrTemplateNode will be translated to Jcr Nodes.

Downstream projects can inject any JcrTemplateNode they want.

Part 2. HST / CMS changes

Originally the plan was to get the available XPageLayout instances for
an Experience Page folder via getting hold of the right Channel and on
the Channel object we would get #getXpageLayouts.

However, this turned out to be problematic: Namely, all Channel objects are
loading actively when loading the HST Model, BUT the Hst Configurations
(HstSite) PER Channel are loaded lazily and on request. However, the
XPageLayout objects would need the 'hst:xpages' section from the hst
channel configuration to be loaded, which is however only loaded as part of
the HstSite. Storing the XPageLayout objects in a Channel object could thus
only be done by killing the lazy loading of HstSite objects, which is not
an option.

A second problem was that typically the cms user adding a new XPage document
is not allowed to read the hst XPage layout configuration nodes at all. That
would then have to be done by some other jcr session.

Also, during a single request, all objects resulting from hst configuration
should have the lifecycle of the HST Model itself

For the above reasons, it was clear that the way to go forward was:

1. Not exposing XPageLayout objects any more via Channel since simply not
   possible
2. During Hst Model HstComponentConfigurationService instance loading,
   directly for XPage layout pages load the JcrTemplateNode for such an
   XPage HstComponentConfigurationService instance and make sure this
   JcrTemplateNode is sealed (aka immutable)
3. To the ChannelService, add the method

   Map<String, XPageLayout> getXPageLayouts(String channelId);
   

   which gives the CMS the possibility to invoke the following code:

   final ChannelService channelService = HippoServiceRegistry
                      .getService(PlatformServices.class).getChannelService();
   final Map<String, XPageLayout> xPageLayouts = channelService.getXPageLayouts(channelId);
   

Only TODO is to support mixins in JcrTemplateNodeConverter which requires
mixin support on HstNode