Add Waveform player to the external libs

[scruffian]

I'm not sure if this is the best way to add this, or if there's a process that generates it.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props scruffian.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[sirreal]

I'm not familiar with maintaining this myself, but I had copilot research and it says this is the right thing to do.

Looks good to me.

[SergeyBiryukov]

Thanks for the PR! Merged in r15091.