Use Qt's High-DPI scaling on Windows

[Nerixyz]

Description

This switches from manual DPI handling to Qt's DPI handling, as Qt 6 disabled the option to opt-out of high DPI scaling through application attributes. Although this PR mainly fixes Windows bugs, it should be tested on all platforms, as the changes will affect everyone.

Windows now mostly uses the display scaling other platforms used.

You can test the scaling for yourself by setting QT_SCALE_FACTOR to something other than 1.

I'm waiting for #3690 to be merged, as that will fix some font-bugs (although I didn't see any on this branch). This PR should be merged first.

• Fixes Display Scaling on Windows in Qt6 Builds is Broken #4552.
• Fixes Scaling broken for message and emote context menus in 2.4.6 #4862.
• Fixes Chatterino window is too tall (for other apps) on Windows #5048.
• I'm pretty sure Startup size scaling issue #2348 will be fixed as well.
• Emote autocomplete list isn't scaling with scale/hidpi #3754 on Windows
• Radio buttons on Join Channel-dialog don't scale up on high DPI systems #754 on Windows
• Context Menu for chats has too large font size on high DPI systems #752 on Windows
• Emote selection window has very small initial size on high-DPI monitors #750 on Windows
• DPI Scaling: Text input box too large on high-DPI screens #749 on Windows
• X button in full screen does not work on far top right corner with windows scaling #5072 should be fixed (?)

I left out "fixes" for some issues, as they might persist on other platforms.

Stuff to test

One major thing to look out for is the size of the window reported to the OS. You can use something like ShareX to measure the size. Make sure the size is exact (not too large, not too small). Previously, the window was 1px too tall. Some of the testing might need to be done on Qt 5.15 or 6.7 (or later).

• Check borders on Windows 11 (are they needed?, is the window cut off?)
  • There seems to be a 1-2px border, however, due to QTBUG-124250 we can't adjust the border (yet... 🙏)
• Check resizing on Windows 11 (is it janky?)
• Dragging a window across screens
• Saving the position on high-dpi screens (Startup size scaling issue #2348)

[github-actions]

clang-tidy made some suggestions

[pajlada]

Dragging Chatterino between two monitors with different scaling works fine for me on Windows 11

[pajlada]

Works much better on Windows now 👍