CENTRAL_LINK_COUNT, ifdef NRF52

Thanks - you too!

What does CENTRAL_LINK_COUNT stand for ?

It's the number of available 'Central' (eg. Espruino connecting to another device) links supported at one time - currently only 1 or 0 is supported - so yes, it's basically just GATT_CLIENT_ENABLED

"ifdef" : "NRF52,ESP32"

This sounds like a good plan - if there's something that could be common then I'd add new functions to bluetooth.h, but I think otherwise just having the ifdef inside jswrap_bluetooth.c isn't too bad.

different naming ... I wonder if there is a general naming convention.

I doubt it :) I guess to avoid as much confusion as possible I'd stick with the naming that's used for the JS APIs themselves - but I know that may not be the case at the moment :)