DataGrid freezes the app on macOS

[Xiaoy312]

Describe the bug

The DataGrid control will cause the app to freeze on macOS once its ItemsSource is populated.
The control will be stuck indefinitely between the MeasureOverride and ArrangeOverride.

Steps to Reproduce

Steps to reproduce the behavior:

• Add a DataGrid to a page.
• Databind or Set its ItemsSource (note: there are loading issue with ItemsSource)

  you can either populate as the page loads, or on button press

• Launch the app, and navigate to that page.
• Press the button if you've added one
• Notice the app stopped responding

Expected behavior

The app should not freeze.

Screenshots

n/a

Environment

NuGet Package(s):

<PackageReference Include="Uno.Microsoft.Toolkit.Uwp.UI.Controls" Version="6.1.0-build.186.g928c99f74d" />
<PackageReference Include="Uno.Microsoft.Toolkit.Uwp.UI.Controls.DataGrid" Version="6.1.0-build.186.g928c99f74d" />

Device form factor:
- [x] macOS
- [ ] WASM
- [ ] iOS (?: not tested)
- [ ] Android (?: not tested)
- [ ] UWP

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

Additional context

n/a