Color palette: Design updates

[kellychoffman]

Suggested improvements for 5.9

• Add borders to the colour circles in the palettes (so the white color is seen).
• Global Styles: improvements to color picker design #36542
• Reposition the “Reset” button (Fix confusing ellipsis menu for the Custom Color Palette feature #36519)
• Never show “core” to a user, use “default” instead. Color UI component: reorder palettes and update names (core by defaults, user by custom) #36622
• Palettes should be reordered by theme, default, user. Color UI component: reorder palettes and update names (core by defaults, user by custom) #36622
• In the styles sidebar, in the color submenu, in the uncommon event there are no colour palettes (see image below), there should be an indicator or CTA so that users don’t need to manually navigate deep into the menus to add colours. Add button text when no colors found #36684
• The counter should count all the colors (default, theme, custom) and not only custom.
• Show gradients and allow to edit them.
• Show duotones (not editable yet).
• Call them "palettes" not "color palettes".

PR for this started here: #36243

[kellychoffman]

Reference image for when there is no color palettes:

[mtias]

And the target design reference:

[oandregal]

#36622 fixed Never show “core” to a user, use “default” instead and Palettes should be reordered by theme, default, user.

Note that the mockups use "Custom" instead of "User" so I did that as well.