add test

test/css/samples/attribute-selector-word-arbitrary-whitespace/expected.css

@@ -0,0 +1 @@
+.foo.svelte-xyz{color:red}[class~="bar"].svelte-xyz{background:blue}

test/css/samples/attribute-selector-word-arbitrary-whitespace/input.svelte

@@ -0,0 +1,13 @@
+<div class="
+foo
+bar
+"></div>
+
+<style>
+	.foo {
+		color: red;
+	}
+	[class~="bar"] {
+		background: blue;
+	}
+</style>