Expect a compile error when class binding name is empty

**Is your feature request related to a problem? Please describe.**
Yes. Sometimes dev's maybe thought that this is a bug

**Describe the solution you'd like**
The compiler should give a compile error


**Additional context**
```svelte
<h1 class:={true}>Hello!</h1>
```
https://svelte.dev/repl/4afa49d00f544af18d89594881340a54?version=3.31.2