Dock and App icons visual enhancement for Round style

[maria-komarova]

A couple changes to the dock and app icon styling specifically for Round style to make the spacing less tight and more visually pleasing:

• change app icon (and minimized window thumbnails as well) horizontal padding from @space_xxs to @space_xs (12 instead of 8),
• add @space_xxxs (4) padding to the dock container (on all sides).

[kleenleen]

Not just for round style, the highlight reaching the edge makes it look broken for square and slightly rounded style too.

Also to mention, there are some misalignments for left and right dock size.

[jacobgkau]

@kleenleen I think the changes requested by the UX team in this issue are being implemented in #482.

The misalignment is being fixed. However, the highlight will still reach the edge when set to square (I think simply because we don't have to worry about corner radii matching as much in square, as both the highlight and the dock are squared off). Personally, I think it looks better that way, but it does seem like it could maybe be a different setting instead of being tied to the squareness.