doc: improve Buffer's encoding documentation

- Add a paragraph about case-insensitivity of encoding options.
- Document "utf-8", "utf-16le" and "ucs-2" aliases.
- Always use "utf8" in documentation for defaults and examples.

PR-URL: #37945
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/buffer.md

@@ -79,17 +79,21 @@ console.log(Buffer.from('fhqwhgads', 'utf16le'));
 // Prints: <Buffer 66 00 68 00 71 00 77 00 68 00 67 00 61 00 64 00 73 00>
 ```
 
+Node.js buffers accept all case variations of encoding strings that they
+receive. For example, UTF-8 can be specified as `'utf8'`, `'UTF8'` or `'uTf8'`.
+
 The character encodings currently supported by Node.js are the following:
 
-* `'utf8'`: Multi-byte encoded Unicode characters. Many web pages and other
-  document formats use [UTF-8][]. This is the default character encoding.
-  When decoding a `Buffer` into a string that does not exclusively contain
-  valid UTF-8 data, the Unicode replacement character `U+FFFD` � will be used
-  to represent those errors.
+* `'utf8'` (alias: `'utf-8'`): Multi-byte encoded Unicode characters. Many web
+  pages and other document formats use [UTF-8][]. This is the default character
+  encoding. When decoding a `Buffer` into a string that does not exclusively
+  contain valid UTF-8 data, the Unicode replacement character `U+FFFD` � will be
+  used to represent those errors.
 
-* `'utf16le'`: Multi-byte encoded Unicode characters. Unlike `'utf8'`, each
-  character in the string will be encoded using either 2 or 4 bytes.
-  Node.js only supports the [little-endian][endianness] variant of [UTF-16][].
+* `'utf16le'` (alias: `'utf-16le'`): Multi-byte encoded Unicode characters.
+  Unlike `'utf8'`, each character in the string will be encoded using either 2
+  or 4 bytes. Node.js only supports the [little-endian][endianness] variant of
+  [UTF-16][].
 
 * `'latin1'`: Latin-1 stands for [ISO-8859-1][]. This character encoding only
   supports the Unicode characters from `U+0000` to `U+00FF`. Each character is
@@ -132,11 +136,11 @@ The following legacy character encodings are also supported:
 * `'binary'`: Alias for `'latin1'`. See [binary strings][] for more background
   on this topic. The name of this encoding can be very misleading, as all of the
   encodings listed here convert between strings and binary data. For converting
-  between strings and `Buffer`s, typically `'utf-8'` is the right choice.
+  between strings and `Buffer`s, typically `'utf8'` is the right choice.
 
-* `'ucs2'`: Alias of `'utf16le'`. UCS-2 used to refer to a variant of UTF-16
-  that did not support characters that had code points larger than U+FFFF.
-  In Node.js, these code points are always supported.
+* `'ucs2'`, `'ucs-2'`: Aliases of `'utf16le'`. UCS-2 used to refer to a variant
+  of UTF-16 that did not support characters that had code points larger than
+  U+FFFF. In Node.js, these code points are always supported.
 
 ```js
 Buffer.from('1ag', 'hex');
@@ -900,7 +904,7 @@ Returns `true` if `encoding` is the name of a supported character encoding,
 or `false` otherwise.
 
 ```js
-console.log(Buffer.isEncoding('utf-8'));
+console.log(Buffer.isEncoding('utf8'));
 // Prints: true
 
 console.log(Buffer.isEncoding('hex'));

doc/api/http.md

@@ -2323,7 +2323,7 @@ changes:
 -->
 
 * `chunk` {string | Buffer}
-* `encoding` {string} Optional, **Default**: `utf-8`
+* `encoding` {string} Optional, **Default**: `utf8`
 * `callback` {Function} Optional
 * Returns: {this}
 
@@ -2565,7 +2565,7 @@ changes:
 -->
 
 * `chunk` {string | Buffer}
-* `encoding` {string} **Default**: `utf-8`
+* `encoding` {string} **Default**: `utf8`
 * `callback` {Function}
 * Returns {boolean}
 

doc/api/stream.md

@@ -2759,7 +2759,7 @@ const fs = require('fs');
 
 pipeline(
   fs.createReadStream('object.json')
-    .setEncoding('utf-8'),
+    .setEncoding('utf8'),
   new Transform({
     decodeStrings: false, // Accept string input rather than Buffers
     construct(callback) {