[js] Outdated Javascript API externs

Recently I had to use the `js.html.audio.AudioBuffer` class and noticed an absence of some fields, in my case [`baseLatency`](https://developer.mozilla.org/en-US/docs/Web/API/AudioContext/baseLatency) and [`outputLatency`](https://developer.mozilla.org/en-US/docs/Web/API/AudioContext/outputLatency). Looking at the `js.html` package on GitHub reveals that most classes haven't been updated in 6 years.

Are there plans to update the externs? Are the externs even automated anymore? I see a lot of files mention being automatically generated, but there have also been pull requests that manually add new features so I'm a bit confused on how it works

The issue points to the js.html package and js.html.audio.AudioBuffer; begin by tracing how these externs are maintained and whether the generated-file notes still apply. Compare the current API fields with the linked MDN reference, then consider the work complete when the maintenance path is clear and the requested latency fields are represented consistently.

Written by the indexing model from the issue text.