Add Tappable to widget.Slider

[alexballas]

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

I was not able to click on slider to quickly move it. I had to drag it instead.

Is it possible to construct a solution with the existing API?

No response

Describe the solution you'd like to see.

A solution where widget.Slider implements the fyne.Tappable interface and properly handles the scroll positioning when tapping on it.

[alexballas]

Since this is now merged, I'm closing it