Due to a change happened via #26102 to make the nested source consistent
with or without source filtering, the _source of a nested inner hit was
always wrapped in the parent path. This turned out to be not ideal for
users relying on the nested source, as it would require additional parsing
on the client side. This change fixes this, the _source of nested inner hits
is now no longer wrapped by parent json objects, irregardless of whether
the _source is included as is or source filtering is used.
Internally source filtering and highlighting relies on the fact that the
_source of nested inner hits are accessible by its full field path, so
in order to now break this, the conversion of the _source into its binary
form is performed in FetchSourceSubPhase, after any potential source filtering
is performed to make sure the structure of _source of the nested inner hit
is consistent irregardless if source filtering is performed.
PR for #26944Closes#26944
87c9b79b10