feat(parsely): Add a fail() parser

I've found this useful for stubbing out parts of a grammar during
development.

Author: AtkinsSJ

packages/phoenix/packages/parsely/exports.js

@@ -1,6 +1,6 @@
 import { adapt_parser, VALUE } from './parser.js';
 import { Discard, FirstMatch, Optional, Repeat, Sequence } from './parsers/combinators.js';
-import { Literal, None, StringOf, Symbol } from './parsers/terminals.js';
+import { Fail, Literal, None, StringOf, Symbol } from './parsers/terminals.js';
 
 class ParserWithAction {
     #parser;
@@ -81,6 +81,7 @@ export class GrammarContext {
 export const standard_parsers = () => {
     return {
         discard: Discard,
+        fail: Fail,
         firstMatch: FirstMatch,
         literal: Literal,
         none: None,

packages/phoenix/packages/parsely/parsers/terminals.js

@@ -91,3 +91,14 @@ export class None extends Parser {
         return { status: VALUE, $: 'none', $discard: true };
     }
 }
+
+/**
+ * Always fails parsing.
+ */
+export class Fail extends Parser {
+    _create () {}
+
+    _parse (stream) {
+        return UNRECOGNIZED;
+    }
+}