Graph controls don't support XY Focus

## Describe the bug
The LoginButton and PeoplePicker Graph controls don't work at all when using XY navigation.

- [ ] Is this bug a regression in the toolkit? If so, what toolkit version did you last see it work:

## Steps to Reproduce
Steps to reproduce the behavior:
1. [Create blank app](https://docs.microsoft.com/en-us/windows/uwp/xbox-apps/development-environment-setup#create-your-first-app)
1. [Add Graph controls](https://github.com/windows-toolkit/Graph-Controls#-getting-started)
1. [Disable mouse mode](https://docs.microsoft.com/en-us/windows/uwp/xbox-apps/how-to-disable-mouse-mode)
1. [Run on an Xbox One console](https://docs.microsoft.com/en-us/windows/uwp/xbox-apps/development-environment-setup#create-your-first-app)
1. Attempt to use the controls with a gamepad

## Expected behavior
The controls should be functional.

## Screenshots
If applicable, add screenshots to help explain your problem.

## Environment

```
NuGet Package(s):

Package Version(s):

Windows 10 Build Number:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [X] May 2019 Update (18362)
- [ ] Insider Build (build number: )

App min and target version:
- [ ] Fall Creators Update (16299)
- [ ] April 2018 Update (17134)
- [ ] October 2018 Update (17763)
- [X] May 2019 Update (18362)
- [ ] Insider Build (xxxxx)

Device form factor:
- [ ] Desktop
- [X] Xbox
- [ ] Surface Hub
- [ ] IoT

Visual Studio
- [ ] 2017 (version: )
- [X] 2019 (version: )
- [ ] 2019 Preview (version: )

```

## Additional context
Add any other context about the problem here.

首先，在禁用鼠标模式的 Xbox One 上的空白应用中按照列出的复现步骤操作，然后检查 LoginButton 和 PeoplePicker Graph 控件。在所述的 Windows 10 环境中，两个控件都能通过基于游戏手柄的 XY 导航正常工作，即表示完成。

由索引模型根据 Issue 内容生成。