XAML: keep HTML entities instead of converting them to unicode.

We are trying out the XAML formatting, but our glyphs get updated to unicode characters.

Is this expected behavior, or a bug?

**Input:**
```<FontIcon x:Name="StartIcon" FontSize="12" Glyph="&#xEDDC;" Foreground="Transparent" />```

**Output:**
```<FontIcon x:Name="StartIcon" FontSize="12" Glyph="" Foreground="Transparent" />```

**Expected behavior:**
To not change this to a unicode character