7c9c2207d0cd66a6ef7c54f107b314f17080e9de  [CMake] Fix missing includes and namespace qualification exposed by a non-unified build - DOMNode, JSVirtualMachine, etc.

Classified as not security-relevant.
Triage note: Adds #include HeapInlines.h / Event.h and qualifies VideoEncodedData as WebCore::VideoEncodedData in RemoteVideoCodecFactory. Pure build/plumbing change with no behavioral effect.
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), surgical (+1.3)