Sample Display Options

In the doc tag for samples:

```
> [!SAMPLE ContentSizerTopShelfPage]
```

We should have a way to specify if we only want C# or XAML displayed

```
> [!SAMPLE ContentSizerTopShelfPage Show="XAML"]
```

Where `Show` can be `XAML`, `C#`, or `All` for instance.

Would provide us some flexibility in scoping to what's interesting or being able to write UI to showcase more C# API focused examples without showing all the UI that's not the interesting bit.

This'll also help us when we go to dump the info to format things properly for static doc generation.

We also have an issue around how large each sample area takes within the docs (or when in the TabbedPage), though we may want a simple issue for that? I don't think we want that to be configured but either fixed or dynamic within the app?