Move color presets into the palette view

[richtabor]

As a follow-up to #56622, I'd like to propose a bit different experience in order to better support themes with many color presets: moving these presets within the palette control.

These color presets change the palette, which changes the colors applied to elements; they are effectively alternate color palettes.

Why

• Allows for the experience to scale better for themes that bundle lots of colors.
• Allows for color presets to render all available colors, giving the user a better understanding of the color palette; not just the body, text, and button colors.
• Selecting a color preset also resets custom colors (at least currently). You can't tell this is happening in trunk, as custom colors are not visible from this top-level view.

Proposal

color-presets.mp4

Current

Currently we have alternate colors presets listed at the top-level in Styles > Colors. While this works for themes with a few color variations, it does not scale all that well, pushing the palette and elements controls out of the way.

Tasks

• Change "X colors" to "Edit Palette"
• Update the "Palette" panel header to match, "Edit Palette"
• Add improved list of color presets below custom colors.

[richtabor]

A minor tweak could be to carry the visual language of the color palette options, as rounded options: