fix: use default cookie decoder (#13037)

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

.changeset/plenty-oranges-count.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: do not override default cookie decoder to allow users to override the `cookie` library version

packages/kit/src/runtime/server/cookie.js

@@ -67,8 +67,7 @@ export function get_cookies(request, url, trailing_slash) {
 				return c.value;
 			}
 
-			const decoder = opts?.decode || decodeURIComponent;
-			const req_cookies = parse(header, { decode: decoder });
+			const req_cookies = parse(header, { decode: opts?.decode });
 			const cookie = req_cookies[name]; // the decoded string or undefined
 
 			// in development, if the cookie was set during this session with `cookies.set`,
@@ -95,8 +94,7 @@ export function get_cookies(request, url, trailing_slash) {
 		 * @param {import('cookie').CookieParseOptions} opts
 		 */
 		getAll(opts) {
-			const decoder = opts?.decode || decodeURIComponent;
-			const cookies = parse(header, { decode: decoder });
+			const cookies = parse(header, { decode: opts?.decode });
 
 			for (const c of Object.values(new_cookies)) {
 				if (