Add link underline color setting in editor for text blocks

[jessica-townsend]

Background

We need a way to set link underline colors from the editor. Currently, the underline color comes from the link's text color and has an opacity value added through JS in the parent theme: https://github.com/thoughtis/cata/blob/master/assets/src/js/modules/text-decoration.js

Acceptance Criteria

• Editors can adjust the link underline color separately from the link color
• The color selection for the link underlines comes from the theme.json color palette
• Fading the underline color will need to be done in the Cata theme

Resources

• https://developer.wordpress.org/block-editor/reference-guides/filters/block-filters/#blocks-registerblocktype
• https://developer.wordpress.org/block-editor/reference-guides/filters/block-filters/#editor-blockedit
• https://developer.wordpress.org/block-editor/reference-guides/components/color-palette/
• https://developer.wordpress.org/block-editor/reference-guides/components/color-picker/
• https://developer.wordpress.org/block-editor/reference-guides/packages/packages-hooks/
• https://github.com/wpcomvip/shopcatalog/tree/516a859ef63d913da34428d4778908ccc28b9b06/plugins/shopcatalog-block-editor/controls/font-family
  

[douglas-johnson]

I thought this was relevant here: https://developer.wordpress.org/news/2023/11/how-to-add-custom-color-options-to-blocks/