RFR: 8337279: Optimize format instant [v4]

[Shaojin Wen]

On Sun, 11 Aug 2024 10:13:35 GMT, Stephen Colebourne <scolebourne at openjdk.org> wrote:

> A more productive direction might be to move `LocalDate.formatTo` and `LocalTime.formatTo` to a JDK internal class (eg. in `jdk.internal.util`?), and then edit `LocalTime.formatTo` to handle `fractionalDigits` directly as another method parameter. This would allow the formatters in `DateTimeFormatterBuilder` to directly use the `formatTo` methods without adding any new public APIs.

I prefer to provide JavaTimeAccess in SharedSecrets, which will require less changes. This depends on https://github.com/openjdk/jdk/pull/20368

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PR Comment: https://git.openjdk.org/jdk/pull/20353#issuecomment-2282729464