Use IDWriteFontFallback to determine font fallback on Windows

The current Windows font database implementation seem to just try all the fonts alphabetically in the system, this leads to various bugs when there are custom fonts installed by various software, e.g I've seen reports about small Thai letters and about invisible letters, all of which seem to come from the fact Qt picks up these broken fonts as they report they support those scripts. There's API since Windows 8.1 to get the system fallback.

https://learn.microsoft.com/en-us/windows/win32/api/dwrite_2/nn-dwrite_2-idwritefontfallback
https://learn.microsoft.com/en-us/windows/win32/DirectWrite/idwritefactory2-getsystemfontfallback
https://learn.microsoft.com/en-us/windows/win32/api/dwrite_2/nf-dwrite_2-idwritefontfallback-mapcharacters