Prior to this issue, SPR-15920 added this new `close()` method which was
supposed to be called to clean resources after response processing.
This commit changes the meaning of that method: calling `close()` will
close the underlying HTTP connection. This has to be called if the
response body is not consumed by the application, since at that point
the underlying connection might be in an inconsistent state if shared in
a connection pool.
Issue: SPR-15993
10139d42fc