gui: Fix fractional scaling for dialog sizes

[cyrossignol]

This provides a workaround to scale the application's GUI dialogs to the appropriate sizes on desktops with fractional DPI scaling. Using 125% scaling on Windows, for example, Qt does not adjust the coordinate system until versions 5.14 and later so dialogs appear cramped and may obstruct the visibility of the contents.

This solution applies manual scaling to render the expected dialog sizes until we can require a minimum Qt version that fully supports fractional scaling.

Some of the application's dialogs have grown quite large over time to accommodate scaling for high-DPI screens. I adjusted dialog sizes to appear no larger than 960x700 logical pixels for reasonable support of a larger number of common resolutions. While many folks use high-resolution displays these days, and extremely small displays are not really a high-priority audience, popular tablet hybrids and inexpensive wide-screen laptops often impose a size challenge for at least one axis. Since this PR alleviates high-DPI issues, we can better support users with lower resolutions by using more typical dialog sizes. The proposed constraint is based on a logical resolution of 1024x768 with some allowance for system UI elements.

As part of this change, I tweaked the UTXO consolidation wizard layouts to respond to the dialog size and adjustments.

Closes #1958.

[jamescowens]

You are a multiple of 5 guy I see... :)

Seriously. I will test this on my different platforms today, since I have a variety of regular and HiDPI screens across different platforms. I agree this deserves to go in Ingrid. The regression risk from a functional point of view is nearly zero, and the benefits appearance-wise merit not waiting until the next release.

[jamescowens]

This is much improved, although with testing, now that the size is much more uniform across the different platforms and resolutions/scale factors, I think the dialog sizes could actually be tweaked down a little bit more even. (With some Linux high dpi displays, the dialog sizes were already smaller compared to the text size before this change. Now they are much bigger and closer to what we have been getting on Windows.) I think this is fine to merge as is, but we may want to do more tweaking on this in the future.

[jamescowens]

ACK