n-api: create napi_env as a real structure

1. We define struct napi_env__ to include the isolate, the last
exception, and the info about the last error.

2. We instantiate one struct napi_env__ during module registration and
we pass it into the FunctionCallbackInfo for all subsequent entries into
N-API when we create functions/accessors/finalizers.

Once module unloading will be supported we shall have to delete the
napi_env we create during module init.

There is a clear separation between public and private API wrt. env:

1. Public APIs assert that env is not nullptr as their first action.

2. Private APIs need not validate env. They assume it's not nullptr.

PR-URL: https://github.com/nodejs/node/pull/12195
Fixes: https://github.com/nodejs/abi-stable-node/issues/198
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

test/addons-napi/test_napi_status/binding.gyp

@@ -0,0 +1,8 @@
+{
+  "targets": [
+    {
+      "target_name": "test_napi_status",
+      "sources": [ "test_napi_status.cc" ]
+    }
+  ]
+}

test/addons-napi/test_napi_status/test.js

@@ -0,0 +1,8 @@
+'use strict';
+
+const common = require('../../common');
+const addon = require(`./build/${common.buildType}/test_napi_status`);
+const assert = require('assert');
+
+addon.createNapiError();
+assert(addon.testNapiErrorCleanup(), 'napi_status cleaned up for second call');

test/addons-napi/test_napi_status/test_napi_status.cc

@@ -0,0 +1,47 @@
+#include <node_api.h>
+
+#define DECLARE_NAPI_METHOD(func) \
+  { #func, func, 0, 0, 0, napi_default, 0 }
+
+void createNapiError(napi_env env, napi_callback_info info) {
+  napi_status status;
+  napi_value value;
+  double double_value;
+
+  status = napi_create_string_utf8(env, "xyz", 3, &value);
+  if (status != napi_ok) return;
+
+  status = napi_get_value_double(env, value, &double_value);
+  if (status == napi_ok) {
+    napi_throw_error(env, "Failed to produce error condition");
+  }
+}
+
+void testNapiErrorCleanup(napi_env env, napi_callback_info info) {
+  napi_status status;
+  const napi_extended_error_info *error_info = 0;
+  napi_value result;
+
+  status = napi_get_last_error_info(env, &error_info);
+  if (status != napi_ok) return;
+
+  status = napi_get_boolean(env, (error_info->error_code == napi_ok), &result);
+  if (status != napi_ok) return;
+
+  napi_set_return_value(env, info, result);
+}
+
+void Init(napi_env env, napi_value exports, napi_value module, void* priv) {
+  napi_status status;
+
+  napi_property_descriptor descriptors[] = {
+      DECLARE_NAPI_METHOD(createNapiError),
+      DECLARE_NAPI_METHOD(testNapiErrorCleanup)
+  };
+
+  status = napi_define_properties(
+    env, exports, sizeof(descriptors) / sizeof(*descriptors), descriptors);
+  if (status != napi_ok) return;
+}
+
+NAPI_MODULE(addon, Init)