UI elements very large on Linux HIDPI

[redthing1]

Describe the bug
The size of UI elements on my HIDPI screen are very large, probably unnecessarily doubled in size.
See screenshots for more info.

To Reproduce
Steps to reproduce the behavior:

1. Run the XAML Controls Gallery on a Linux system with X, with DPI set to 192
2. Observe that everything is really big.

Expected behavior
See screenshots: I expect the ui element size when running the application to be more reasonable, i.e. matching their size previewer there.

Screenshots
It looks fine in the previewer (ignore the background image, it's my IDE theme):

However this very same application is now huge (this shows comparison)

But when I run the application:

Desktop (please complete the following information):

• OS: Arch Linux, X with DPI set to 192
• Version 0.10.0-rc1

Additional context
N/A

[redthing1]

Here, for comparison, is the same thing running on a non-HIDPI system (which configuration and OS wise is identical to the other):

Here it can be seen that the application matches the previewer in size.

[maxkatz6]

#4826

[redthing1]

Oh, that solves my issue. Thank you!