Ensure appropriate labels are provided for color/gradient picker controls

[andrewhayward]

What problem does this address?

Changes introduced in #52255 make it a requirement for the CircularOptionPicker to have an aria-label/-labelledby prop provided, to make sure appropriate context is available for the control. The three consuming components (ColorPalette, DuotonePicker and GradientPicker) all hide this requirement behind a default value, and should transition away from optional ARIA props to requiring a label of some sort.

What is your proposed solution?

All of the higher-order controls that use these three foundational components should be updated to provide a more appropriate and relevant label for their context, passing either an aria-label or aria-labelledby prop.

Acceptance Criteria

• [x] Identify all of the controls that use ColorPalette, DuotonePicker and GradientPicker
• [ ] Update them to provide context-appropriate labels with aria-label or aria-labelledby
• [ ] Update ColorPalette, DuotonePicker and GradientPicker to require one of aria-label or aria-labelledby (see related conversation)

[andrewhayward]

Components that use <ColorPalette>:

• [ ] Block Editor ColorGradient
• [ ] Block Library CoverEdit
• [ ] Block Library native CoverEdit
• [ ] Components BorderControl/BorderControlDropdown
• [x] Components DuotonePicker/ColorListPicker

  54468

• [ ] Components native mobile/ColorSettings
• [ ] Components PaletteEdit
• [ ] Format Library TextColor/ColorPicker

[andrewhayward]

Components that use <DuotonePicker>:

• [x] Block Editor DuotoneControl

  54473

• [ ] Block Editor GlobalStyles/FiltersPanel
• [ ] Edit Site GlobalStyles/GradientPalettePanel

[andrewhayward]

Components that use <GradientPicker>:

• [ ] Block Editor ColorsGradients/ColorGradientControl
• [ ] Components PaletteEdit