Editor: add support for block-level link hover colors.

Adds the ability to set link hover colors for individual blocks from the block inspector color panel.

Props @youknowriad, @peterwilsoncc, @kebbet.
Fixes #58575.


git-svn-id: https://develop.svn.wordpress.org/trunk@56028 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/theme.json

@@ -11,6 +11,8 @@
 		},
 		"color": {
 			"background": true,
+			"button": true,
+			"caption": true,
 			"custom": true,
 			"customDuotone": true,
 			"customGradient": true,
@@ -121,6 +123,7 @@
 					"slug": "midnight"
 				}
 			],
+			"heading": true,
 			"link": false,
 			"palette": [
 				{