[css-grid-3][masonry] Make item-tolerance initial value normal #12111
Description
https://drafts.csswg.org/css-grid-3/#item-slack
With the latest resolution of using item-tolerance and making the item-* properties work differently in multiple layout types, it would make sense to change the initial value of this property to normal, following the similar behavior of [column|row]-gap.
Currently, only masonry has a use for item-tolerance, but it could potentially be reused elsewhere, while the normal behavior for masonry container can be kept as 1em for placement ties.