assert: refactor internal assert.js

Move lib/internal/assert.js to lib/internal/assert/assertion_error.js.
This is in preparation for making lib/internal/assert.js a tiny module
for use in Node.js built-ins so that we can use `assert()` without
having to load the entire ~1200 line `assert` module.

PR-URL: #25956
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>

lib/assert.js

@@ -27,7 +27,7 @@ const { codes: {
   ERR_INVALID_ARG_VALUE,
   ERR_INVALID_RETURN_VALUE
 } } = require('internal/errors');
-const { AssertionError } = require('internal/assert');
+const AssertionError = require('internal/assert/assertion_error');
 const { openSync, closeSync, readSync } = require('fs');
 const { inspect, types: { isPromise, isRegExp } } = require('util');
 const { EOL } = require('internal/constants');

lib/internal/assert.js → lib/internal/assert/assertion_error.js

@@ -405,6 +405,4 @@ class AssertionError extends Error {
   }
 }
 
-module.exports = {
-  AssertionError
-};
+module.exports = AssertionError;

node.gyp

@@ -84,7 +84,7 @@
       'lib/vm.js',
       'lib/worker_threads.js',
       'lib/zlib.js',
-      'lib/internal/assert.js',
+      'lib/internal/assert/assertion_error.js',
       'lib/internal/async_hooks.js',
       'lib/internal/bash_completion.js',
       'lib/internal/buffer.js',