src: include node_api_types.h instead of node_api.h in node.h

Including `node.h` should not result in all of Node-API also being
available to callers. Users who want `node_api.h` contents should
explicitly include that header.

We currently include it specifically for `napi_addon_register_func`;
by moving that into `node_api_types.h` and including that instead,
we can reduce unintentionally included API surface a lot.

Refs: #60345 (comment)

Author: addaleax

src/node.h

@@ -76,7 +76,7 @@
 #include "v8-platform.h"  // NOLINT(build/include_order)
 #include "node_version.h"  // NODE_MODULE_VERSION
 
-#include "node_api.h"
+#include "node_api_types.h"  //  napi_addon_register_func
 
 #include <functional>
 #include <memory>

src/node_api.h

@@ -33,10 +33,6 @@ struct uv_loop_s;  // Forward declaration.
 #define NAPI_NO_RETURN
 #endif
 
-typedef napi_value(NAPI_CDECL* napi_addon_register_func)(napi_env env,
-                                                         napi_value exports);
-typedef int32_t(NAPI_CDECL* node_api_addon_get_api_version_func)(void);
-
 // Used by deprecated registration method napi_module_register.
 typedef struct napi_module {
   int nm_version;

src/node_api_types.h

@@ -3,6 +3,10 @@
 
 #include "js_native_api_types.h"
 
+typedef napi_value(NAPI_CDECL* napi_addon_register_func)(napi_env env,
+                                                         napi_value exports);
+typedef int32_t(NAPI_CDECL* node_api_addon_get_api_version_func)(void);
+
 typedef struct napi_callback_scope__* napi_callback_scope;
 typedef struct napi_async_context__* napi_async_context;
 typedef struct napi_async_work__* napi_async_work;