e9945d774ab64ddbe74baaf887c1cce1dc678b46  [Safer CPP] Address uncounted local variable warnings in Source/WebCore/dom

Classified as not security-relevant.
Triage note: Blanket SaferCPP hardening: raw `Node*`/`protect()` loops in ContainerNode::moveBefore, Element::topmostPopoverAncestor and Position.cpp's nextRenderedEditable/previousRenderedEditable/enclosingVisualBoundary are rewritten to RefPtr, and the files are dropped from UncheckedLocalVarsChecker/UncountedLocalVarsChecker expectations. No specific UAF or bug is identified in the message or diff; per rubric this is a false positive.
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 (+6.47), area:Source/WebCore/dom (+2.0), surgical (+1.3)