RFR: 8337832: Optimize datetime toString

[Chen Liang]

On Sat, 27 Jul 2024 13:45:11 GMT, Shaojin Wen <duke at openjdk.org> wrote:

> Similar to PR #20321, this improves performance by providing a method that passes in a StringBuilder to avoid unnecessary object allocation.

Since I am not responsible for the date time area, I would prefer @naotoj who's more familiar to review too.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20368#pullrequestreview-2259239088