Page Root Provider Fallback for Experience Fragments

[HitmanInWis]

The original PageRootProvider was written before Experience Fragments were prominent. When the PageRootProvider attempts to get a root page for an Experience Fragment, it cannot find it. This leads to the following downsides:

• Shared Component Properties render from the XF folder root rather than the rendered site. They are also stored there when authoring XF. This creates duplicate, potentially differing values from component instances in the site page tree and component instances within XF.
• Contextual Pathbrowser (from ACS AEM Commons) cannot be effectively used in components with XF, as the page root cannot be determined.
• Any other site functionality that wants to get the site homepage is unable to do so reliably with PageRootProvider

We should update the current PageRootProvider to check for a fallbackPageRoot property in the resource inherited properties. This would allow a property of fallbackPageRoot="/content/mysite/en" in the folder root of XF, which would then cause all uses of PageRootProvider to return the website homepage.

Since this would only work in cases where the XF folder defines the property, it would be backward compatible with legacy implementations. It would just give a new option for people that want their site to store/use Shared Component Properties and get the "homepage" using PageRootProvider from their site directly.