Add HiDPI theme for better scaling, hi-res displays

[newhoa]

Previously, in #455, I was going to add HiDPI simply as a build option. This, instead, simply installs the HiDPI version by default, alongside the standard PNG theme. This will add a few MB to the package size, and about 50MB to the install size. It was mentioned in Shimmer Project discussion that this way would make it more accessible to users and easier for package maintainers who didn't want to have to deal with the build option or separate packages (and these benefits would outweigh the disk size increase).

I think this makes more sense, especially with Xfce 4.19+ supporting HiDPI icons by default, I think users will not want to search hard or use a build option for these.

@ochosi, let me know if you are okay with this way of adding HiDPI. Thanks!

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Install SVG-based HiDPI theme alongside the PNG-based theme. This should be used for better icon scaling, specifically when Scaling is set to 2x or 3x. PNG may be a bit faster to load, so the SVG HiDPI theme is optional.

Using the HiDPI theme will fix issues where the wrong icons are shown in some places with scaling enabled (like the Places sidebars in file managers). It should also fix and blurry icon issues, especially with scaling enabled. The PNG non-HiDPI theme restricted the amount of zoom steps the icons had in file managers with scaling enabled, so this should resolve that as well.

Fixes #124
Fixes #317
Fixes #362
Fixes #403

[bluesabre]

Works as expected. Should elementary-xfce Dark get the same treatment?

[newhoa]

Works as expected. Should elementary-xfce Dark get the same treatment?

Thank you for checking/testing!

We've been moving toward deprecating and removing the Dark theme. The "colorize" PRs replace the faux-symbolic icons in both the light and dark themes with fullcolor icons (now that symbolic icons are an option for developers, forcing/faking the look seemed unnecessary or wrong). Once the "colorize" PRs are merged, Dark will basically be an empty theme with the unified fullcolor icons in the main theme.

So, if the above it okay with you, I think holding off on this HiDPI PR until there is only the unified main theme would make sense?

I'm afraid it would be inconvenient for users to have Dark and Dark HiDPI in one release only to be removed in the following release.

Let me know what you think. I'm happy to do whatever makes the most sense or whatever is best needed!

[bluesabre]

That sounds reasonable to me. Keep on with the colorized PRs and we can merge everything at once (or when you feel good about them).