add test for validating tag definition

test/validator/samples/dinamic-element-invalid-tag/errors.json

@@ -0,0 +1,15 @@
+[{
+	"code": "missing-element-definition",
+	"message": "<svelte:element> must have a 'this' attribute",
+	"start": {
+		"line": 2,
+		"column": 1,
+		"character": 7
+	},
+	"end": {
+		"line": 2,
+		"column": 1,
+		"character": 7
+	},
+	"pos": 7
+}]

test/validator/samples/dinamic-element-invalid-tag/input.svelte

@@ -0,0 +1,3 @@
+<div>
+	<svelte:element>foo</svelte:element>
+</div>