fix: make param matcher generated type import with a .js extension (#…

…13286)

fixes #13280

Similar to #5907 we need to import the param matchers file ending with .js so that when the moduleResolution is set to something strict such as NodeNext (the default for libraries) the type inference isn't lost when it can't resolve the param matcher file due to the lack of a file extension.

.changeset/slimy-cows-listen.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: make param matchers generated type import end with `.js`

packages/kit/src/core/sync/write_types/index.js

@@ -585,7 +585,7 @@ function replace_ext_with_js(file_path) {
 function generate_params_type(params, outdir, config) {
 	/** @param {string} matcher */
 	const path_to_matcher = (matcher) =>
-		posixify(path.relative(outdir, path.join(config.kit.files.params, matcher)));
+		posixify(path.relative(outdir, path.join(config.kit.files.params, matcher + '.js')));
 
 	return `{ ${params
 		.map(