"NAPI_EXPERIMENTAL is enabled" when building addons against node v25.0.0

[mscdex]

Seeing as how node core is currently unconditionally doing #define NAPI_EXPERIMENTAL, this is unnecessary noise when building (especially addons).

I suggest one of the following:

• Moving the define to a separate file to isolate it to just the code that is using the experimental parts (that are not used by addons).
• Moving the define to the node gyp file that only gets set when building node itself (and not addons).
• Remove the compiler warning message entirely.

[szegedi]

Even worse for us at https://github.com/DataDog/pprof-nodejs as we build with -Werror.