Surface Dial Extension Bugs

## Describe the bug
Found a few issues with the Surface Dial TextBox Extensions:

- [ ] Tapping doesn't go to the next control (if you have focus on first box below, tap dial, then it doesn't go to next textbox)
- [x] ~Default Icon should be `Scroll` not `Ruler` as it is shown in menu (unlike the comment says) and...~ (didn't notice we're going to have scroll already by default, so I guess ruler is a good compromise unless we added a custom icon...
- [ ] Is `ForceMenuItem` required for this to work? It seems to be which is odd...
- [ ] Copy the TextBox in the sample and you'll see there's two (or more!) menu items in the Surface Menu... (there should only ever be a single one).


## Steps to Reproduce

Sample App:
```xml

```

## Expected behavior
Tapping should go to the next tab order control. Menu item should only appear a single time ever when the textbox has focus. If it can work without the `ForceMenuItem` property it should, otherwise this property seems useless, should it just be `ShowMenuItem`?

## Environment
Existing 6.1 Sample App.

Start with the Existing 6.1 Sample App and reproduce the unchecked SurfaceDialTextbox behaviors using the provided XAML: tap navigation, ForceMenuItem handling, and duplicate menu items. Inspect the SurfaceDialTextbox extension entry points and attached properties mentioned in the sample. Done means tapping advances to the next tab-order control and the focused TextBox contributes only one correctly configured menu item.

Scritto dal modello di indicizzazione a partire dal testo della issue.