Support Node-API modules declaring their "Node-API version"

[kraenhansen]

Node-API modules can declare a version that they want to be initialized with, either:

• By setting nm_version in the napi_module passed to napi_module_register (depends on Support module registration via calls to napi_module_register #3).
• By exporting a node_api_module_get_api_version_v1 function (of type node_api_addon_get_api_version_func).

As per https://nodejs.org/docs/latest/api/n-api.html#node-api-version-matrix I believe this should default to 8 if not explicitly provided by the addon.

Blocked on an upstream Hermes change

Since we moved to Hermes' first-party Node-API implementation, the addon's Node-API version is Hermes' to act on, and its public API currently offers no way to set it:

• napi_env__::module_api_version is a fixed member initialized to NAPI_VERSION (API/napi/hermes_napi_impl.h), and nothing assigns it afterwards.
• hermes_napi_create_env(void *hermes_runtime, hermes_napi_host *host) takes no version, so an embedder cannot pass one in.
• hermes_napi_load_module() — which we now use to load addons — does not look up node_api_module_get_api_version_v1, nor read nm_version off the module it falls back to.

The version is not inert in Hermes: API/napi/hermes_napi_reference.cpp branches on env->module_api_version < 10 for reference semantics, so an addon declaring version 8 is currently served version-10 behavior.

Detecting the version on our side is easy (dlsym the symbol, or read nm_version), but there is nowhere to put the answer. So this needs one of the following upstream in facebook/hermes first, and an issue should be opened there:

1. hermes_napi_load_module() reads node_api_module_get_api_version_v1 (falling back to nm_version, then to 8) and sets module_api_version on the env itself — matching what Node does in napi_module_register_by_symbol. Preferred: it keeps the detection next to the loading, so every embedder gets it right.
2. Failing that, a way for the embedder to set it — an extra parameter on a hermes_napi_create_env variant, or a setter — so we can detect the version ourselves and pass it in.

Worth flagging in that upstream issue: Hermes defaults to NAPI_VERSION (the newest version it implements) where Node.js defaults an addon that declares nothing to 8, so the default is a compatibility difference on its own, independent of which option above is taken.