fix(node_http2): keep header validation enabled (#36042)
- treat the shared HTTP/2 option flags as option-presence bits only
- apply native option values only when their corresponding presence bit
is set
- keep nghttp2 HTTP messaging validation enabled for ordinary session
options
- add raw-client coverage for the option-buffer behavior
The JavaScript side records which numeric options are present in a
shared flags field. The native side previously also interpreted two of
those bits as unrelated nghttp2 behavior flags. This change separates
those meanings and prevents stale shared-buffer values from affecting
sessions that did not set the corresponding option.
