Function invoke

invoke(wgt, func, ...rargs): void
Invokes the specified method of the specified widget. In other words, it is similar to execute the following:
```
wgt[func].apply(wgt, vararg);
```
Parameters
- wgt: Widget<HTMLElement>
  the widget to invoke
- func: string
  the function name
- Rest ...rargs: unknown[]
  any number of arguments passed to the function invocation.
Returns void