src: update NODE_MODULE_VERSION to 84

Major V8 updates are usually API/ABI incompatible with previous
versions. This commit adapts NODE_MODULE_VERSION for V8 8.3.

Refs: https://github.com/nodejs/CTC/blob/master/meetings/2016-09-28.md

PR-URL: nodejs#32831
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/abi_version_registry.json

@@ -1,5 +1,6 @@
 {
   "NODE_MODULE_VERSION": [
+    { "modules": 84, "runtime": "node", "variant": "v8_8.3", "versions": "15.0.0-pre" },
     { "modules": 83, "runtime": "node",     "variant": "v8_8.1",               "versions": "14.0.0" },
     { "modules": 82, "runtime": "electron", "variant": "electron",             "versions": "10" },
     { "modules": 81, "runtime": "node",     "variant": "v8_7.9",               "versions": "14.0.0-pre" },

src/node_version.h

@@ -89,7 +89,7 @@
  * version matching should open a pull request to reserve a number in this
  * registry.
  */
-#define NODE_MODULE_VERSION 83
+#define NODE_MODULE_VERSION 84
 
 // The NAPI_VERSION provided by this version of the runtime. This is the version
 // which the Node binary being built supports.