Frame and outline color consistency and high-contrast setting changes

Here's a todolist for all the items that need to be fixed and modified to make all separators and such consistent between applications.

• Set colors to share same values plasma/breeze!395 (merged)
• Breeze separator/outline color fixes plasma/breeze!396 (merged)
• Kirigami outline/separator colors frameworks/kirigami!1453 (merged) and frameworks/kirigami!1462 (merged)
• qqc2-desktop-style outline/separator colors frameworks/qqc2-desktop-style!361 (merged) and frameworks/qqc2-desktop-style!364 (merged)
• Kirigami addons libraries/kirigami-addons!219 (merged)
• breeze gtk plasma/breeze-gtk!85 (merged)
• breeze plasma theme plasma/libplasma!1055 (merged)
• High contrast frames setting (Accessibility KCM)
  • XDG portal has now high contrast setting support, so I think this could be in accessibility settings, and breeze theme just checks that and changes the outline intensity accordingly.

Currently most colors are set either with separatorColor = alphaColor(foregroundColor, opacity) or KColorUtils::Mix(foreground, background, bias).

Bias and opacity are pretty much the same thing here, so here's the changes I've made:

• Plasma 5 bias/opacity: 0.25
• Plasma 6 contrast value: 0.20
• High contrast bias/opacity: this will be automatically calculated to be AAA contrast value

We also need to make kirigami and qqc2-desktop-style follow the high contrast setting if it's enabled.

I copied the explanation and reasoning for these changes from one of the older merge requests (plasma/breeze!393) here:

The current frame coloring is quite intense, adding to the "heaviness" of the look.

What we could do is make the frames less intense by default, but give user the ability to set the frames to a higher contrast color with a checkbox.

If this change goes through, I will also modify the window outlines to follow same settings.

This will also help in future if we decide to make the separator/outline colors customizable. But I think even modifying the intensity of them will be very helpful for keeping Breeze looking fresh, yet allowing the high-contrast theme users set it brighter.

The high contrast setting will be in the Accessibility KCM