Intent to ship: Joint Iteration

[Daniel Minor]

As of Firefox 148, I intend to enable the Joint Iteration proposal by default on all platforms. It is currently available in Nightly builds, but disabled by default and controlled by the `javascript.options.experimental.joint_iteration` preference. The proposal adds new `Iterator.zip` and `Iterator.zipKeyed` methods that allow zipping together underlying iterators into an iterator over values grouped by position, similar to zip in many other languages. Our implementation was contributed by André Bargull, thank you!

The proposal reached Stage 3 of the TC39 process at the November 2025 plenary, Safari has started their implementation (https://bugs.webkit.org/show_bug.cgi?id=303246), work does not appear to have started in Chromium (https://issues.chromium.org/issues/465357675).

Bug to turn on by default: https://bugzilla.mozilla.org/show_bug.cgi?id=2003333

Standard: https://github.com/tc39/proposal-joint-iteration