Global Styles: Add button to reset color palette

[jorgefilipecosta]

This PR adds a button that allows users to reset user changes to the color palette, making the color palette have the theme or core defaults again.

How has this been tested?

I went to the edit site screen, global styles sidebar.
I made some changes to the color palette and I verified I could reset the changes using the reset button that is available.

[github-actions]

Size Change: +54 B (0%)

Total Size: 1.19 MB

Filename	Size	Change
build/components/index.js	171 kB	+31 B (0%)
build/components/style-rtl.css	15.3 kB	+6 B (0%)
build/components/style.css	15.3 kB	+5 B (0%)
build/edit-site/index.js	23.3 kB	+12 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.14 kB	0 B
build/annotations/index.js	3.77 kB	0 B
build/api-fetch/index.js	3.42 kB	0 B
build/autop/index.js	2.84 kB	0 B
build/blob/index.js	664 B	0 B
build/block-directory/index.js	8.71 kB	0 B
build/block-directory/style-rtl.css	943 B	0 B
build/block-directory/style.css	942 B	0 B
build/block-editor/index.js	133 kB	0 B
build/block-editor/style-rtl.css	11.3 kB	0 B
build/block-editor/style.css	11.3 kB	0 B
build/block-library/editor-rtl.css	8.91 kB	0 B
build/block-library/editor.css	8.92 kB	0 B
build/block-library/index.js	147 kB	0 B
build/block-library/style-rtl.css	8.1 kB	0 B
build/block-library/style.css	8.1 kB	0 B
build/block-library/theme-rtl.css	792 B	0 B
build/block-library/theme.css	793 B	0 B
build/block-serialization-default-parser/index.js	1.87 kB	0 B
build/block-serialization-spec-parser/index.js	3.06 kB	0 B
build/blocks/index.js	48 kB	0 B
build/compose/index.js	9.9 kB	0 B
build/core-data/index.js	14.8 kB	0 B
build/data-controls/index.js	821 B	0 B
build/data/index.js	8.74 kB	0 B
build/date/index.js	11.2 kB	0 B
build/deprecated/index.js	768 B	0 B
build/dom-ready/index.js	571 B	0 B
build/dom/index.js	4.92 kB	0 B
build/edit-navigation/index.js	11.1 kB	0 B
build/edit-navigation/style-rtl.css	881 B	0 B
build/edit-navigation/style.css	885 B	0 B
build/edit-post/index.js	306 kB	0 B
build/edit-post/style-rtl.css	6.51 kB	0 B
build/edit-post/style.css	6.49 kB	0 B
build/edit-site/style-rtl.css	3.98 kB	0 B
build/edit-site/style.css	3.98 kB	0 B
build/edit-widgets/index.js	26.3 kB	0 B
build/edit-widgets/style-rtl.css	3.16 kB	0 B
build/edit-widgets/style.css	3.16 kB	0 B
build/editor/editor-styles-rtl.css	476 B	0 B
build/editor/editor-styles.css	478 B	0 B
build/editor/index.js	42.5 kB	0 B
build/editor/style-rtl.css	3.85 kB	0 B
build/editor/style.css	3.85 kB	0 B
build/element/index.js	4.62 kB	0 B
build/escape-html/index.js	735 B	0 B
build/format-library/index.js	6.86 kB	0 B
build/format-library/style-rtl.css	547 B	0 B
build/format-library/style.css	548 B	0 B
build/hooks/index.js	2.16 kB	0 B
build/html-entities/index.js	623 B	0 B
build/i18n/index.js	3.57 kB	0 B
build/is-shallow-equal/index.js	698 B	0 B
build/keyboard-shortcuts/index.js	2.52 kB	0 B
build/keycodes/index.js	1.94 kB	0 B
build/list-reusable-blocks/index.js	3.1 kB	0 B
build/list-reusable-blocks/style-rtl.css	476 B	0 B
build/list-reusable-blocks/style.css	476 B	0 B
build/media-utils/index.js	5.32 kB	0 B
build/notices/index.js	1.79 kB	0 B
build/nux/index.js	3.4 kB	0 B
build/nux/style-rtl.css	671 B	0 B
build/nux/style.css	668 B	0 B
build/plugins/index.js	2.56 kB	0 B
build/primitives/index.js	1.43 kB	0 B
build/priority-queue/index.js	790 B	0 B
build/redux-routine/index.js	2.84 kB	0 B
build/reusable-blocks/index.js	3.05 kB	0 B
build/rich-text/index.js	13.3 kB	0 B
build/server-side-render/index.js	2.77 kB	0 B
build/shortcode/index.js	1.69 kB	0 B
build/token-list/index.js	1.27 kB	0 B
build/url/index.js	4.05 kB	0 B
build/viewport/index.js	1.84 kB	0 B
build/warning/index.js	1.14 kB	0 B
build/wordcount/index.js	1.22 kB	0 B

_{compressed-size-action}

[aristath]

Sync'd with the master branch. Without pulling latest commits from master I was getting an infinite-recursion PHP error and was unable to test this.

[aristath]

LGTM 👍