Add the html to the willPaste event details

The fragment is still the important thing, but this lets the willPaste
handler look at the original HTML as part of its processing too.

source/Editor.ts

@@ -1061,6 +1061,7 @@ class Squire {
                 const event = new CustomEvent('willPaste', {
                     cancelable: true,
                     detail: {
+                        html,
                         fragment: frag,
                     },
                 });