[lworld] RFR: Use stringStream to keep field layout output together.

[Frederic Parain]

On Fri, 14 Jun 2024 18:43:56 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> Tested with -XX:+PrintFieldLayout comparing before and after, and field_layout tests.
> 
>    TEST                                              TOTAL  PASS  FAIL ERROR   
>    jtreg:test/hotspot/jtreg/runtime/valhalla/inlinetypes/field_layout
>                                                          6     6     0     0

LGTM.
Thank you Coleen for this nice cleanup of the ttyLock.

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Marked as reviewed by fparain (Committer).

PR Review: https://git.openjdk.org/valhalla/pull/1132#pullrequestreview-2119140546