chore: [#1947] Adds unit tests for decode ' / numeric character references in attr values (#1948)

- attribute values can contain named and numeric character references
  per https://html.spec.whatwg.org/multipage/syntax.html#syntax-attribute-value
- add decoding for all numeric character references
- add decoding for ', this could probably appear in single-quoted
  attribute values
- ignore other named character references, the list is huge

Co-authored-by: David Ortner <david@ortner.se>

Author: cgoetz-inovex

packages/happy-dom/test/html-parser/HTMLParser.test.ts

@@ -2256,6 +2256,21 @@ describe('HTMLParser', () => {
             `);
 		});
 
+		it('Handles numeric character references and ' in attribute values for #1947', () => {
+			const result = new HTMLParser(window).parse(`
+                <div>
+                    <span data-foo="&#34;"></span>
+                    <span data-foo="&#x22;"></span>
+                    <span data-foo="&apos;"></span>
+                </div>`);
+			expect(new HTMLSerializer().serializeToString(result)).toBe(`
+                <div>
+                    <span data-foo="&quot;"></span>
+                    <span data-foo="&quot;"></span>
+                    <span data-foo="'"></span>
+                </div>`);
+		});
+
 		it('Handles numeric character references in attribute values for #1947', () => {
 			// Decimal numeric character reference
 			const result1 = new HTMLParser(window).parse(`<div data-foo="&#34;"></div>`);