Windows font scaling is not respected

**Describe the bug**
When the system font size is changed, only the window name and the menu fontsize are updated correctly.

**To Reproduce**
1. run application with briefcase dev
2. change font scaling in windows settings

**Expected behavior**
All items in the frame should adapt the new font size

**Screenshots**
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**Environment:**
- Operating System: Windows 10
- Python version: 3.8.5
- Software versions:
- briefcase==0.3.3
- toga-core==0.3.0.dev22
- toga-winforms==0.3.0.dev22

**Additional context**
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Start by reproducing the issue with `briefcase dev` on Windows 10, then inspect the font-scaling path used by the Toga WinForms backend. Compare the window name and menu updates with other frame items when Windows font scaling changes. Done means all items in the frame adapt to the new system font size.

Written by the indexing model from the issue text.