G'MIC host dialog does not support HDPI

[EricGrange]

When opening on a 4k monitor with 200% font scaling, G'MIC opens without any scaling, so the text is very tiny. When moving the dialog to a secondary monitor with 125% scaling, only the filters list becomes readable (I suspect this is unintentional, the rest of the text is further downscaled, so it still unreadable)

Below is a screenshot on a 4K monitor at 200% (check dialog caption title characters for the size text should have)

Same dialog moved from 4k monitor at 200% to a secondary monitor at 125%

[amyspark]

I think the attribute Qt::AA_EnableHighDpiScaling needs to be set (not sure if pixmaps need to be adjusted too, I don't have a HiDPI screen on my Linux box to test):

https://github.com/c-koi/gmic-qt/blob/d824a99d2ab1803842fe29e5ca633257e19bca13/src/GmicQt.cpp#L546-L552