UI, CodeDiffDialog: Fix table widget display issues, including dark style.

[TryTwo]

Before:

After:

Note that the top header text is no longer being cutoff.

Would help if people could test this. I don't know what window uses sorting arrows and I was just focused on fixing this one window.

I suggest adding dark.qss to the Styles folder for easy switching.

[TryTwo]

@AdmiralCurtiss Can you confirm these dark.qss changes?

[TryTwo]

If that (record) button fix is too random, I can move it elsewhere.

[TryTwo]

@dreamsyntax I thought setting the record button fixed worked, but it still pops. I missed it, wasn't checking at the right time. Looks like the problem is setting the border size in the custom pushed stylesheet that's in codediff. I think setting it fixes it in the regular style, lol.

[dreamsyntax]

@dreamsyntax I thought setting the record button fixed worked, but it still pops. I missed it, wasn't checking at the right time. Looks like the problem is setting the border size in the custom pushed stylesheet that's in codediff. I think setting it fixes it in the regular style, lol.

I'm not too worried about that. The white block in dark theme is more relevant anyway.

[TryTwo]

Sorry for being so pushy, but I think I wrangled it into submission.

[dreamsyntax]

Works good on Windows light/dark theme.
Latest commit resolves
#12265 (comment)