use `Array.from` to report string length.

This is another fix to better support multi-byte emoji

src/threads.js

@@ -4344,7 +4344,7 @@ Process.prototype.reportStringSize = function (data) {
     if (data instanceof List) { // catch a common user error
         return data.length();
     }
-    return isNil(data) ? 0 : data.toString().length;
+    return isNil(data) ? 0 : Array.from(data.toString()).length;
 };
 
 Process.prototype.reportUnicode = function (string) {