require whitespace after `{@html` (#2154)

src/parse/state/mustache.ts

@@ -316,6 +316,8 @@ export default function mustache(parser: Parser) {
 		}
 	} else if (parser.eat('@html')) {
 		// {@html content} tag
+		parser.requireWhitespace();
+
 		const expression = readExpression(parser);
 
 		parser.allowWhitespace();

test/parser/samples/raw-mustaches-whitespace-error/error.json

@@ -0,0 +1,10 @@
+{
+	"code": "missing-whitespace",
+	"message": "Expected whitespace",
+	"start": {
+		"line": 1,
+		"column": 6,
+		"character": 6
+	},
+	"pos": 6
+}

test/parser/samples/raw-mustaches-whitespace-error/input.svelte

@@ -0,0 +1 @@
+{@htmlfoo}