Although we index block.height for blocks in the KV indexer, this reserved
attribute was not previously exposed to the event subscription API. Despite
being advertised in the OpenAPI spec, neither the old (websocket) nor new
(events) query interface could see it. This change exposes block.height to the
/events API.
In addition: Remove a non-public constant from types (finalize_block). This
value is used only as an internal tag by the indexer, and should not be exposed
to users of the public interface. (We could probably drop it entirely, as it
was previously a disambiguator for BeginBlock vs. EndBlock events, but keeping
a tag here simplifies the cleanup).
b5550b0d1b