[filter-effects-1] color-interpolation-filters can affect feOffset

[litherum]

https://drafts.fxtf.org/filter-effects/#ColorInterpolationFiltersProperty

The note says:

The color-interpolation-filters property just has an affect on filter operations. Therefore, it has no effect on filter primitives like <feOffset> ...

In feOffset, the dx and dy values don't have to be integral, which means it may perform interpolation between adjacent pixels. Interpolation is sensitive to color space. I think <feOffset> actually can be sensitive to color-interpolation-filters.

[longsonr]

In Firefox, at least we convert dx and dy to integers before we do anything with them.