d9714228c9f87cd777e4106916ee38087b9e0e49  [SVG2] Implement the path attribute on <textPath>

Classified as not security-relevant.
Triage note: Adds SVGTextPathElement m_pathAttribute parsing plus RenderSVGTextPath::usesPathAttribute()/layoutPath() and computeTextPathStartOffset() to honor inline path data per spec; new feature.
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 (+4.87), null_guard (+1.2), msg_medium (+2.0), msg_soft (+1.0), msg_noise (-2.5), area:Source/WebCore/svg (+2.0)