Refactor logic for each registry we create specialized indexing support for

[lightwalker-eth]

Background

1. We already created a class / interface for modeling registries: SupportedNFTIssuer in the Tokenscope plugin.
2. In PR 1196 we are expanding the customized logic for registries, including:
   1. Getting the registry's managed name.
   2. tokenIdToLabelHash
   3. Potentially others.

Goals

Refactor code referenced above in the "Background" so that it is better unified together and so that each registry we implement special logic for has all of that special logic centralized into a single place and not spread across multiple places in our code.