🏷️ Add overload for Clipboard.dangerouslyPasteHTML()

`Clipboard.dangerouslyPasteHTML()` is allowed to be called without an
index as its first argument.

At the moment, doing this results in a compilation error:

```
(method) Clipboard.dangerouslyPasteHTML(index: number, html: string, source?: EmitterSource): void
Expected 2-3 arguments, but got 1.ts(2554)
```

This change adds the overload to allow this.

modules/clipboard.ts

@@ -130,9 +130,15 @@ class Clipboard extends Module<ClipboardOptions> {
     );
   }
 
+  dangerouslyPasteHTML(html: string, source?: EmitterSource): void;
   dangerouslyPasteHTML(
     index: number,
     html: string,
+    source?: EmitterSource,
+  ): void;
+  dangerouslyPasteHTML(
+    index: number | string,
+    html: string,
     source: EmitterSource = Quill.sources.API,
   ) {
     if (typeof index === 'string') {