71e49219a946696fc857961ec57e1d20a9b3cfb0  [line-clamp] Floats paint past the block-end content edge of the line-clamp container

Classified as not security-relevant.
Triage note: Adds LineClampUpdater::isInsideLineClampContainer/blockEndClipRect and applies the clip in RenderBlockFlow::paintFloats and RenderLayer clip-rect computation so floats of a line-clamp container are clipped to its block-end content edge. New rendering behavior per spec, not a bug fix.
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), null_guard (+1.95), msg_medium (+2.0), msg_soft (+1.0), msg_noise (-2.5), area:Source/WebCore/layout (+2.0)