Changed the error message to be more descriptive

Added test

src/compiler/parse/state/tag.ts

@@ -333,7 +333,7 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 			if (name === null) {
 				parser.error({
 					code: 'empty-attribute-value',
-					message: 'Empty attribute shorthand'
+					message: 'Attribute shorthand cannot be empty'
 				}, start);
 			}
 

test/parser/samples/error-empty-attribute-shorthand/error.json

@@ -0,0 +1,10 @@
+{
+    "code": "empty-attribute-value",
+    "message": "Attribute shorthand cannot be empty",
+    "start": {
+        "line": 1,
+        "column": 6,
+        "character": 6
+    },
+    "pos": 6
+}

test/parser/samples/error-empty-attribute-shorthand/input.svelte

@@ -0,0 +1 @@
+<span {}></span>