build,deps: refactor and fix v8.gyp

* Make inspector.gypi and v8_external_snapshot.gypi includible targets.
* Make `v8_dump_build_config` an action
* Better separate `js2c` and `natives_blob`
* process action outputs as sources
* trigger v8.gyp:postmortem-metadata from v8.gyp

PR-URL: https://github.com/nodejs/node/pull/23182
Refs: https://github.com/nodejs/node/pull/23156


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>