chore(build): Update compiler & linter input language to ES2020 (#5745)

Also:

- Ensure that the `comma-dangle` rule will not be applied to
function parameter lists (even when multi-line).

- Update tests/node/.eslintrc.json to make the environment
node-specific and not pinned to es6.

tests/node/.eslintrc.json

@@ -1,8 +1,6 @@
 {
-    "parserOptions": {
-        "ecmaVersion": 6
-    },
     "env": {
+        "node": true,
         "browser": false,
         "mocha": true
     },