Use the same type for SearchRequest's body and MultisearchBody

[swallez]

SearchRequest body and MultisearchBody have exactly the same properties. They should actually be the same type: beyond removing the need to keep them in sync, this also allows using that same type to build both search requests and multisearch request items.

This will be a breaking change since we need to rename MultisearchBody to something like SearchRequestBody and update SearchRequest to use it as a value body.

Reported in elastic/elasticsearch-java#151

[Erkanerkisi]

Hi, Is there any update here?