API to determine if Large Fonts are in use on the device.

### Description

When a user changes their device to large fonts, it typically plays havoc with a nicely built UI. While it's easy to allow some spacing in an app for differing font sizes, a UI will potentially become unusable (or at least hard to navigate) at 2x font size.

I know that the FontAutoScalingEnabled option exists, but that's bad for acessability if you just disable the scaling.

Ideally we should have some ability to query whether the device has large fonts enabled so we can make UI decisions accordingly. Maybe reduce some padding, maybe hide an icon that looks good at normal sizing but isn't imperative to the usage of the app. Maybe enable word wrap in certain areas.

### Public API Changes

``` csharp
if (App.LargeFontsEnabled) {
icon.Visible = false;
}
```

### Intended Use-Case

As described above. We would check if large fonts are in use and alter the UI accordingly to make things more readable.

No implementation file, test, or entry point is named. Start by locating the existing FontAutoScalingEnabled handling and reviewing how font settings are exposed across the supported device platforms. Done means a documented App.LargeFontsEnabled API can reliably report the setting and has coverage for the relevant platforms.

Written by the indexing model from the issue text.