[6.x] Remove overscroll-behavior-x: contain; on panels

[jaygeorge]

Description of the Problem

The UI panel component contains overscroll-x-contain, which disables the browsers default forward/back navigation when hovering over the panel and using a trackpad-like device, even if the panel isn't scrollable.

overscroll-behavior-x: contain;—which prevents scroll chaining for neighboring scrolling areas—may be desirable, but the side effect of disabling native navigation is likely less desirable, especially considering most panels won't be horizontally scrollable anyway.

What this PR Does

• Removes the property, fixing native browser navigation
• Closes Overscroll behaviour on UI panel stops forward/back navigation #14614

How to Reproduce

1. Go to a page that has the panel such as Collections > some collection
2. Hover over the panel and use a native navigation gesture such as swipe left to go back
3. Observe how it will not work when hovering over this UI component