Fix Bug with Continuous Autoscrolling when Smooth Scrolling is Enabled

[regulus79]

Fixing a bug Gabrielxd195 pointed out, where enabling smooth scroll in the song editor causes the view to move at an uneven rate.

This is fixed by setting the scroll value directly through m_leftRightScroll->setValue() instead of using animateScroll().

Also one thing I wanted to point out is that this means there will be no smooth scrolling for continuous autoscrolling whatsoever. So if the view needs to move a long distance to get to the current play position (like if you are editing the end of the song but then play it from the start), then it will do so instantly, without any smooth transition. That's probably fine for most people, but it means that the smooth scroll setting doesn't have any effect for continuous autoscrolling.

Related to #7396

[Gabrielxd195]

@regulus79 Brother, I tried this improvement and I loved it, thank God there were no problems. I had suggested this function in #5010 and thanks to you and the other devs that we now have it available, but please (if it is not too much to ask) before merging make this enabled by default, because it is more modern and less abrupt when making small changes while the song is playing. For my part I am going to close #5010. Thank you

[sakertooth]

Seems like @Gabrielxd195 already tested this and was the original submitter for this issue, so if they are fine with it, so am I (not much to say about the code change to be honest). 👍

[DomClark]

I haven't tested this, nor did I review the original PR, but the change looks reasonable to me.