http2: remove pushValueToArray in Http2Session::HandleHeadersFrame

Instead of calling into JS from C++ to push values into an array,
use the new Array::New API that takes a pointer and a length
directly.

PR-URL: https://github.com/nodejs/node/pull/24264


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>