Is your feature request related to a problem? Please describe.

This task is part of the effort to rework the Starter Page Template Picker for new pages. On a self-hosted site as a user, I should be able to use the new layout picker utilizing the layouts that are currently provided in the existing STP picker.

Goals

• On self-hosted sites, when creating a new page, a user should be presented with the layouts currently used by the existing SPT picker.
  + The format of the existing layouts should be modified to match the scheme as provided by /wpcom/v2/sites/{site}/block-layouts and copied to a place that is accessible by the apps.
  + Ideally these will be moved to a place that can be shared by both iOS and Android then served up through their respective Gutenberg Mobile libraries. However, there shouldn't be an excessive amount of time spent on that aspect. For the first version, we can duplicate the data and improve the reusability later if needed.
  + The existing SPT should still work when this feature is disabled.
  + This data can be used as the static data used to build the UI in [Modal Layout Picker] Create Layout Picker sections and thumbnail UI using static data #2436, and [Modal Layout Picker] Create Layout Picker category bar UI using static data #2437
• The layouts for the self-hosted sites can be fetched from the public API https://public-api.wordpress.com/wpcom/v2/common-block-layouts

Additional context

Blueprint Flow - iOS

Blueprint Flow - Android