4b6b2cdc90927388eb93d81906d4af25e7aa79df  Content changing inside an element with a blur filter doesn't properly repaint

Classified as not security-relevant.
Triage note: Large refactor replacing hasSoftwareFilters with a pixel-moving-filter renderer count, threading RepaintRectsUpdate/ClipRepaintToLayer enums, and splitting shouldPaintWithFilters. The only safety-flavored change is swapping ASSERT(m_filters) for an if(m_filters) guard; no identified memory-safety or logic bug fixed.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+3.0), null_guard (+2.59), area:Source/WebCore/rendering (+2.0)