docs: update code examples for node:url module

There are many things called `url` in this page including `url` module,
`URL` instances, etc.

The original example was not clear where these methods come from.

Author: fisker

doc/api/url.md

@@ -1013,17 +1013,18 @@ This function ensures the correct decodings of percent-encoded characters as
 well as ensuring a cross-platform valid absolute path string.
 
 ```js
-new URL('file:///C:/path/').pathname;    // Incorrect: /C:/path/
-fileURLToPath('file:///C:/path/');       // Correct:   C:\path\ (Windows)
+const url = require('url');
+new URL('file:///C:/path/').pathname;      // Incorrect: /C:/path/
+url.fileURLToPath('file:///C:/path/');     // Correct:   C:\path\ (Windows)
 
-new URL('file://nas/foo.txt').pathname;  // Incorrect: /foo.txt
-fileURLToPath('file://nas/foo.txt');     // Correct:   \\nas\foo.txt (Windows)
+new URL('file://nas/foo.txt').pathname;    // Incorrect: /foo.txt
+url.fileURLToPath('file://nas/foo.txt');   // Correct:   \\nas\foo.txt (Windows)
 
-new URL('file:///你好.txt').pathname;    // Incorrect: /%E4%BD%A0%E5%A5%BD.txt
-fileURLToPath('file:///你好.txt');       // Correct:   /你好.txt (POSIX)
+new URL('file:///你好.txt').pathname;      // Incorrect: /%E4%BD%A0%E5%A5%BD.txt
+url.fileURLToPath('file:///你好.txt');     // Correct:   /你好.txt (POSIX)
 
-new URL('file:///hello world').pathname; // Incorrect: /hello%20world
-fileURLToPath('file:///hello world');    // Correct:   /hello world (POSIX)
+new URL('file:///hello world').pathname;   // Incorrect: /hello%20world
+url.fileURLToPath('file:///hello world');  // Correct:   /hello world (POSIX)
 ```
 
 ### `url.format(URL[, options])`
@@ -1053,6 +1054,7 @@ any way. The `url.format(URL[, options])` method allows for basic customization
 of the output.
 
 ```js
+const url = require('url');
 const myURL = new URL('https://a:b@測試?abc#foo');
 
 console.log(myURL.href);
@@ -1077,16 +1079,17 @@ This function ensures that `path` is resolved absolutely, and that the URL
 control characters are correctly encoded when converting into a File URL.
 
 ```js
-new URL(__filename);                // Incorrect: throws (POSIX)
-new URL(__filename);                // Incorrect: C:\... (Windows)
-pathToFileURL(__filename);          // Correct:   file:///... (POSIX)
-pathToFileURL(__filename);          // Correct:   file:///C:/... (Windows)
+const url = require('url');
+new URL(__filename);                  // Incorrect: throws (POSIX)
+new URL(__filename);                  // Incorrect: C:\... (Windows)
+url.pathToFileURL(__filename);        // Correct:   file:///... (POSIX)
+url.pathToFileURL(__filename);        // Correct:   file:///C:/... (Windows)
 
-new URL('/foo#1', 'file:');         // Incorrect: file:///foo#1
-pathToFileURL('/foo#1');            // Correct:   file:///foo%231 (POSIX)
+new URL('/foo#1', 'file:');           // Incorrect: file:///foo#1
+url.pathToFileURL('/foo#1');          // Correct:   file:///foo%231 (POSIX)
 
-new URL('/some/path%.c', 'file:'); // Incorrect: file:///some/path%.c
-pathToFileURL('/some/path%.c');    // Correct:   file:///some/path%25.c (POSIX)
+new URL('/some/path%.c', 'file:');   // Incorrect: file:///some/path%.c
+url.pathToFileURL('/some/path%.c');  // Correct:   file:///some/path%25.c (POSIX)
 ```
 
 ### `url.urlToHttpOptions(url)`
@@ -1317,6 +1320,7 @@ The `url.format()` method returns a formatted URL string derived from
 `urlObject`.
 
 ```js
+const url = require('url');
 url.format({
   protocol: 'https',
   hostname: 'example.com',