[WASM][Canvas] Sample can go off screen

[StewartPolsky]

Describe the bug

Sample can go off screen

Steps to reproduce the bug

1. Go to https://xamlcontrolsgallery.platform.uno/
2. Click on Layout
3. Click on Canvas
4. Move vertical slider down to the bottom end
5. Move top horizontal slider all the way to the left end
6. Notice that the red square goes out of bounds and is no longer visible

Screenshots

Version Info

Gallery version (found on Settings page):

0.1.0-uno.1+246

Windows 10 version:

• [ ] Insider Build (xxxxx)
• [ ] October 2018 Update (17763)
• [ ] April 2018 Update (17134)
• [ ] Fall Creators Update (16299)
• [ ] Creators Update (15063)
• [ ] Anniversary Update (14393)
• [x] 1909 Build 18363.836

Device form factor:

• [x] Desktop
• [ ] Mobile
• [ ] Xbox
• [ ] Surface Hub
• [ ] IoT

Additional context