Bug 281501 – [JSC] Fix rounding error for `Intl.DurationFormat`

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Sosuke Suzuki]

Our `Intl.DurationFormat` is affected by rounding errors because each unit is summed as a double.
    Additionally, very large values cannot fit within a double.
    
    This patch introduces the following changes:
    
    - Each unit is summed using `Int128`.
    - Since `Int128` values cannot be formatted with ICU’s `unumf_formatDouble`[1], so we build a
      decimal-formatted string from the `Int128` value and use `unumf_formatDecimal`[2] for formatting.
    
    [1]: https://unicode-org.github.io/icu-docs/apidoc/released/icu4c/unumberformatter_8h.html#a54193ed406316485803e3dac3a96615f
    [2]: https://unicode-org.github.io/icu-docs/apidoc/released/icu4c/unumberformatter_8h.html#a6183aa03b43b63b231341770035bace9

[Sosuke Suzuki]

Pull request: https://github.com/WebKit/WebKit/pull/35219

[EWS]

Committed 285482@main (48d36047a83e): <https://commits.webkit.org/285482@main>

Reviewed commits have been landed. Closing PR #35219 and removing active labels.

[Radar WebKit Bug Importer]

<rdar://problem/138261569>