test,doc: make module name match gyp target name

Currently the nm_modname does not match the file name of the resulting
module. In fact, the nm_modname is pretty arbitrary. This seeks to
introduce some consistency into the nm_modname property by having the
name of the module appear in exactly one place: the "target_name"
property of the gyp target that builds the module.

PR-URL: https://github.com/nodejs/node/pull/15209
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/addons/stringbytes-external-exceed-max/binding.cc

@@ -21,4 +21,4 @@ void init(v8::Local<v8::Object> exports) {
   NODE_SET_METHOD(exports, "ensureAllocation", EnsureAllocation);
 }
 
-NODE_MODULE(binding, init)
+NODE_MODULE(NODE_GYP_MODULE_NAME, init)