[BUG] XContentBuilder.toString() will close the builder itself about opensearch

[andrross]

@chishui Thanks for reporting this! I think it is a pretty common with the builder pattern that a builder isn't necessarily mutable after "building" it. It's a fair question as to whether toString-ing the builder should implicitly "build" it. I don't know exactly the specifics here, but in order to avoid this problem you may well have to make a deep copy of the builder state when toString-ing it, which would have performance implications. Would you care to put up a PR attempting to fix this? I would also probably be okay with just explicitly documenting the toString() method as a terminal operation on the builder that closes it. The BytesReference::bytes method is properly documented.

[chishui]

Many implementations neither explicitly call close() nor use try (XContentBuilder buildre = ...), they just return builder.toString(). Seems not feasible to fix all of them, will add a comment for now.