tools,doc: update JavaScript primitive types to match MDN Web Docs

- Update primitive types to lower case, so the anchor of https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Data_structures will work correctly.
- Add `bigint` to primitive types to match MDN Web Doc.

PR-URL: #60581
Reviewed-By: Jordan Harband <ljharb@gmail.com>
Reviewed-By: Claudio Wunder <cwunder@gnome.org>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: JustappleJust

tools/doc/type-parser.mjs

@@ -3,13 +3,14 @@ const jsDocPrefix = `${mdnPrefix}/JavaScript/`;
 
 const jsDataStructuresUrl = `${jsDocPrefix}Data_structures`;
 const jsPrimitives = {
-  boolean: 'Boolean',
-  integer: 'Number', // Not a primitive, used for clarification.
-  null: 'Null',
-  number: 'Number',
-  string: 'String',
-  symbol: 'Symbol',
-  undefined: 'Undefined',
+  boolean: 'boolean',
+  integer: 'number', // Not a primitive, used for clarification.
+  null: 'null',
+  number: 'number',
+  string: 'string',
+  symbol: 'symbol',
+  undefined: 'undefined',
+  bigint: 'bigint',
 };
 
 const jsGlobalObjectsUrl = `${jsDocPrefix}Reference/Global_Objects/`;
@@ -43,7 +44,6 @@ const customTypesMap = {
 
   'AsyncGeneratorFunction': 'https://tc39.es/proposal-async-iteration/#sec-asyncgeneratorfunction-constructor',
 
-  'bigint': `${jsDocPrefix}Reference/Global_Objects/BigInt`,
   'WebAssembly.Instance':
     `${jsDocPrefix}Reference/Global_Objects/WebAssembly/Instance`,
   'WebAssembly.Memory':