rename .html files to .svelte

test/apps/preloading/src/routes/slow-preload.svelte

@@ -0,0 +1,13 @@
+<script context="module">
+	export function preload() {
+		return new Promise(fulfil => {
+			if (typeof window !== 'undefined') {
+				window.fulfil = fulfil;
+			} else {
+				fulfil({});
+			}
+		});
+	}
+</script>
+
+<h1>This page should never render</h1>