[Feature] Different ScrollPhysics for horizontal and vertical scrolling

[sschmaljohann]

Would it be possible to add an option to use different ScrollPhysics for vertical and horizontal scrolling?

In my use-case I have a grid with a constraint width but in an vertical scroll view. With the current implementation I can only set the whole scroll physics to NeverScrollableScrollPhysics, which locks the vertical scroll as needed, but also prevents to horizontal scrolling.

[Wdestroier]

Apparently a duplicate of #96.