Add new setScroll method

[ffxsam]

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Per https://github.com/katspaugh/wavesurfer.js/discussions/3405, it would be great to have a setScroll method (counterpart to getScroll), to be able to programmatically set the scroll position.

I'll likely work on this. Feel free to mark this issue as an enhancement.

[tapeboy7]

I need this too. What about having setScroll forward the command to the private scrollIntoView method in renderer.ts?

[katspaugh]

scrollIntoView won't set the scroll to an arbitrary point, it only makes sure the playhead is visible.

It should be a new renderer method that simply sets this.scrollContainer.scrollLeft.