fix: Hide horizontal volume panel while the slider is not active and mute toggle button is on focus

[mrdtron]

Description

Show horizontal volume panel only when the volume slider is active or volume button is hovered but not when focused. This addresses #4431

Requirements Checklist

• Feature implemented / Bug fixed
• Reviewed by Two Core Contributors

[gkatsev]

Thanks for the PR and your patience. Code-wide, this looks good. Though, I'd like to take it for a spin before merging.

[gkatsev]

Just took a look, this is pretty great. Thanks!
One thing that I noticed is that if you tab to the mute button the volume slider doesn't show, though, not sure if that's a big deal or not. Any thoughts @OwenEdwards?

[mrdtron]

@gkatsev Thanks for reviewing this! I'd personally think that slider should appear only when hovering on the mute toggle button or tabbing into it from the keyboard — a good example of the behaviour is the Youtube player — but I'm open to suggestions.

One issue I noticed just now is that once you mute/unmute volume through keyboard volume slider flickers. Fixing that now.

[gkatsev]

Yeah, I guess it's fine not to open the volume slider via the keyboard when tabbing into the mute toggle, looks fine in youtube.

[gkatsev]

And I confirmed no volume slider flicker when toggling mute.

[brandonocasey]

Nice fix! I think I have seen this but didn't really notice that it was an issue.