Add new APIs to Webamp NPM module

[captbaritone]

TODO

• [x] Validate APIs work in test environment
• [ ] Add to documentation
• [ ] Figure out how we can cut a release with these new APIs given current state of build

Test Plan

Added the following to the demo site:

const LLAMA_TRACK = {
  metaData: {
    artist: "DJ Mike Llama",
    title: "Llama Whippin' Intro",
  },
  url: llamaAudio,
  duration: 5.322286,
};

webamp.onCurrentTrackDidChange((track, index) => {
  const currentTracks = webamp.getPlaylistTracks();
  const willRunOut =
    index === currentTracks.length - 1 &&
    !webamp.isRepeatEnabled() &&
    !webamp.isShuffleEnabled();
  if (willRunOut) {
    webamp.appendTracks([LLAMA_TRACK]);
  }
});

https://github.com/user-attachments/assets/4b101cf4-5861-4377-8a09-fb84939dc7e3

[github-actions[bot]]

Size Change: +315 B (+0.06%)

Total Size: 494 kB

Filename	Size	Change
./packages/webamp/built/webamp.bundle.min.js	304 kB	+170 B (+0.06%)
./packages/webamp/built/webamp.lazy-bundle.min.js	191 kB	+145 B (+0.08%)

_{compressed-size-action}

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[captbaritone]

Shipped in a separate commit and released in v2.1.1

[captbaritone]

Did not ship onCurrentTrackDidChange since I think onTrackDidChange should suffice