Feat: dragstart and dragend events for drag to seek

[brian-byassee]

Short description

Add dragstart and dragend events for drag to seek feature.

Resolves #

Implementation details

Add two new events and updated the functions passed to makeDraggable to make start and end emit the new event

How to test it

http://127.0.0.1:9090/#all-options.js
Add

wavesurfer.on('drag', (x) => console.log('drag',x))
wavesurfer.on('dragstart', (x) => console.log('dragstart',x))
wavesurfer.on('dragend', (x) => console.log('dragend',x))

check box to make Drag to Seek active.

Observe console.

Screenshots

Checklist

• This PR is covered by e2e tests
• It introduces no breaking API changes

[katspaugh]

Thanks! 🚀