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

• 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
• Components DuotonePicker/ColorListPicker
  Ensure that 'Duotone Filter' color pickers have relevant labels #54468
• Components native mobile/ColorSettings
• Components PaletteEdit
• Format Library TextColor/ColorPicker

[andrewhayward]

Components that use <DuotonePicker>:

• Block Editor DuotoneControl
  Adding label/description to BlockEditor/DuotoneControl #54473
• Block Editor GlobalStyles/FiltersPanel
• Edit Site GlobalStyles/GradientPalettePanel

[andrewhayward]

Components that use <GradientPicker>:

• Block Editor ColorsGradients/ColorGradientControl
• Components PaletteEdit