Enhance ExperienceFragments and ExperienceFragmentDataImpl to support microsites

[rdb987]

Feature Request

Is your feature request related to a problem? Please describe.
Is not possible to use Experience Fragments (e.g. for header/footer) for microsites or website that don't use standard ISO codes.

Describe the solution you'd like
It would be nice to have ExperienceFragmentData interface available and not only Implementation class in order to override some specific methods (for example: getLocalizedFragmentVariationPath() to support paths like /content/myproject/global/microsite) with delegation pattern.

Are there alternatives?
The alternative for me for now is simply to copy paste the core component code under our custom repository and simply modify what we need.