There are special rules for blending filter values with accumulation per https://drafts.fxtf.org/filter-effects/#accumulation, we need to implement them.
Pull request: https://github.com/WebKit/WebKit/pull/6739
Committed 256952@main (7b53609d924d): <https://commits.webkit.org/256952@main> Reviewed commits have been landed. Closing PR #6739 and removing active labels.
<rdar://problem/102612383>