Dpi-aware process for Winforms

[obulat]

Currently toga Winforms apps are rendered with 96 dpi, and virtually scaled to higher dpi monitors which makes text and controls appear blurry on high dpi monitors.

This PR sets app process to be dpi aware, which makes texts appear crisper, and makes window size smaller. It is only set so on Windows major versions higher than 6.0 (Windows Vista, apparently).

The change can be seen on this screenshot, the dpi-aware window is on the left, and the previous dpi-non-aware window is on the right.

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

From a quick poke around, it looks like these two lines are added automatically to every new C# application as part of the template, so it makes sense we'd do the same.