[5.x] CP nav reordering fixes

[jesseleite]

It was reported that there was some lingering issues re-ordering CP nav items, partly due to storing preferences in JSON in SQL, but also partly due to some missing implementation.

Todo

• Test and fix issues at NavTransformer level
  • The transformer is what converts the Vue payload to YAML/JSON when storing preferences
• Test and fix issues at NavPreferencesNormalizer level
  • The normalizer is what run when reading YAML/JSON
  • This is important for re-ordering, because we support the old reorder: true boolean for backwards compatibility
• Test and fix issues at NavBuilder level
  • This is where the nav is actually built after reading YAML/JSON and normalizing
  • First the core nav is built, the normalized preferences are applied on top
• Test with TV2