src: get embedder options on-demand

Only query embedder options when they are needed so that the bootstrap
remains as stateless as possible so that the bootstrap snapshot is
controlled solely by configure options, and subsequent runtime changes
should be done in pre-execution.

PR-URL: https://github.com/nodejs/node/pull/40357


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Shelley Vohr <shelley.vohr@gmail.com>