PageBuilderService is not available to plugins since upgrade to Atlassian Plugins Webresource 3.0

See PLUGWEB-72 for additional context.

The Atlassian Webresource 3.0 release notes recommend that when upgrading, the PageBuilderService is a new component that should be wired by the host application.

When Confluence upgraded to WR 3.0, this was not done, and instead Confluence uses a legacy, backwards-compatible constructor in the WebResourceManager that constructs a new instance of the PageBuilderService in-line.

This is problematic for plugin developers as some parts of the old WebResourceManager API are now only available through the new PageBuilderService API, and the PageBuilderService is currently inaccessible to plugins.

To address this, Confluence's should declare the PageBuilderService as a top-level, plugin-available Spring bean, and change Confluence's WebResourceManager to call the correct WebResourceManagerImpl constructor.