doc: mark some node-api functions as experimental

PR-URL: #42987
Reviewed-By: Jiawen Geng <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Darshan Sen <[email protected]>
Reviewed-By: Chengzhong Wu <[email protected]>
Reviewed-By: Michael Dawson <[email protected]>

Author: NickNaso

doc/api/n-api.md

@@ -1187,6 +1187,8 @@ added:
   - v16.14.0
 -->
 
+> Stability: 1 - Experimental
+
 ````c
 NAPI_EXTERN napi_status node_api_throw_syntax_error(napi_env env,
                                                     const char* code,
@@ -1306,6 +1308,8 @@ added:
   - v16.14.0
 -->
 
+> Stability: 1 - Experimental
+
 ```c
 NAPI_EXTERN napi_status node_api_create_syntax_error(napi_env env,
                                                      napi_value code,